Fix possible double-free of temporary indices buffer in compressMG1.c

[musicinmybrain]

This appears to be a clear-cut case of accidentally calling free on a dangling pointer.

GCC reported:

compressMG1.c: In function ‘_ctmCompressMesh_MG1’: compressMG1.c:188:5: warning: pointer ‘indices_45’ may be used after ‘free’ [-Wuse-after-free]
  188 |     free((void *) indices);
      |     ^~~~~~~~~~~~~~~~~~~~~~
compressMG1.c:179:3: note: call to ‘free’ here
  179 |   free((void *) indices);
      |   ^~~~~~~~~~~~~~~~~~~~~~

and indeed, the conditional call to free removed in this PR appears a few lines after an unconditional free in

OpenCTM/lib/compressMG1.c

Line 179 in 91b3b71

free((void *) indices);