pawndisasm: Minor fixes, code cleanup

[Daniel-Cortez]

What this PR does / why we need it:

• Fixed input and output files not being properly closed and code being leaked on early returns.

• Implemented proper handling for invalid instructions.
  Now instead of crashing on invalid instructions (due to OOB access to the opcode table) pawndisasm prints a proper error message with the code of invalid instruction and the address it was detected at.

• Removed extra space after AMX flags.

• Code cleanup.

  • Removed unused data from the opcode table.
    It seems that the opcode table was copied from sc6.c and sorted by opcode IDs instead of alphabetical order, but field OPCODE::opcode was left unused.
  • Removed opcode handler do_switch() (it was a duplicate of do_jump()).
  • Function casetbl() has been renamed into do_casetbl() to be more in-line with the names of the other opcode handlers.

Which issue(s) this PR fixes:

What kind of pull this is:

• A Bug Fix
• A New Feature
• Some repository meta (documentation, etc)
• Other

Additional Documentation:

[Zeex]

👍