Fix "PHP Warning: Undefined array key currentUri" when using @import (inline)

When enabling source maps and an input file uses `@import (inline)`,
then the source map generation causes this error because not all
chunks have file info metadata associated in that case.

This matches upstream behaviour at
* Output Mapped:
  https://github.com/less/less.js/blob/v3.13.1/packages/less/src/less/source-map-output.js#L89
* Generator:
  https://github.com/mozilla/source-map/blob/v0.7.4/lib/source-map-generator.js#L110-L129

Without the changes in lib/, the new test case fails with:

```
1) MapTest::testImportInline
Undefined array key "currentUri"

/less.php/lib/Less/Output/Mapped.php:68
…
/less.php/lib/Less/SourceMap/Generator.php:118
/less.php/lib/Less/Parser.php:235
/less.php/test/phpunit/MapTest.php:37
```

Ref #109.
Closes https://github.com/wikimedia/less.php/pull/121.

Bug: T380641
Change-Id: I2e04e33facd6f900c147c124e9931ffc2cac5551

Author: tck

.editorconfig

@@ -10,6 +10,9 @@ insert_final_newline = true
 [test/phpunit/ParserTest.php]
 trim_trailing_whitespace = false
 
+[test/**/*.map]
+insert_final_newline = false
+
 # Markdown:
 # - Editors should not change leading spaces to tabs (e.g. multi-line list items)
 # YAML:

lib/Less/Output/Mapped.php

@@ -63,8 +63,7 @@ public function add( $chunk, $fileInfo = null, $index = 0, $mapLines = null ) {
 		$sourceLines = [];
 		$sourceColumns = ' ';
 
-		if ( $fileInfo ) {
-
+		if ( isset( $fileInfo['currentUri'] ) ) {
 			$url = $fileInfo['currentUri'];
 
 			if ( isset( $this->contentsMap[$url] ) ) {

lib/Less/SourceMap/Generator.php

@@ -204,10 +204,12 @@ public function addMapping( $generatedLine, $generatedColumn, $originalLine, $or
 			'generated_column' => $generatedColumn,
 			'original_line' => $originalLine,
 			'original_column' => $originalColumn,
-			'source_file' => $fileInfo['currentUri']
+			'source_file' => $fileInfo['currentUri'] ?? null
 		];
 
-		$this->sources[$fileInfo['currentUri']] = $fileInfo['filename'];
+		if ( isset( $fileInfo['currentUri'] ) ) {
+			$this->sources[$fileInfo['currentUri']] = $fileInfo['filename'];
+		}
 	}
 
 	/**

test/Fixtures/less.php/css/T380641-sourcemap-import-inline.map

@@ -0,0 +1 @@
+@import (inline, css) url("imports/a.less");

test/Fixtures/less.php/less/T380641-sourcemap-import-inline.less

@@ -7,15 +7,34 @@ public function testMap() {
 		$expectedFile = self::$fixturesDir . '/bootstrap3-sourcemap/expected/bootstrap.map';
 		$mapDestination = self::$cacheDir . '/bootstrap.map';
 
-		$options['sourceMap'] = true;
-		$options['sourceMapWriteTo'] = $mapDestination;
-		$options['sourceMapURL'] = '/';
-		$options['sourceMapBasepath'] = dirname( dirname( $lessFile ) );
-		$options['math'] = "always";
+		$parser = new Less_Parser( [
+			'sourceMap' => true,
+			'sourceMapURL' => '/',
+			'sourceMapBasepath' => dirname( dirname( $lessFile ) ),
+			'sourceMapWriteTo' => $mapDestination,
+			'math' => 'always',
+		] );
+		$parser->parseFile( $lessFile );
+		$parser->getCss();
+
+		$expected = file_get_contents( $expectedFile );
+		$generated = file_get_contents( $mapDestination );
+		$this->assertEquals( $expected, $generated );
+	}
+
+	public function testImportInline() {
+		$lessFile = self::$fixturesDir . '/less.php/less/T380641-sourcemap-import-inline.less';
+		$expectedFile = self::$fixturesDir . '/less.php/css/T380641-sourcemap-import-inline.map';
+		$mapDestination = self::$cacheDir . '/import-inline.map';
 
-		$parser = new Less_Parser( $options );
+		$parser = new Less_Parser( [
+			'sourceMap' => true,
+			'sourceMapURL' => '/',
+			'sourceMapBasepath' => dirname( $lessFile ),
+			'sourceMapWriteTo' => $mapDestination,
+		] );
 		$parser->parseFile( $lessFile );
-		$css = $parser->getCss();
+		$parser->getCss();
 
 		$expected = file_get_contents( $expectedFile );
 		$generated = file_get_contents( $mapDestination );