Use delete[] to free new[]-allocated buffer in decodeJPEGIntoSurface OOM path

[iurisilvio]

Fixes #2573.

Image::decodeJPEGIntoSurface allocates a buffer with new uint8_t[] and frees it with free() on the OOM error path — undefined behavior in C++ (new[] and free() may use different allocators, and even when they share one they may have different bookkeeping for the array size header).

Every other deallocation of new uint8_t[] buffers in Image.cc (lines 710, 898, 901, 991) already uses delete[] correctly; this is the only outlier. Caught by g++ -Wmismatched-new-delete:

../src/Image.cc:844:9: warning: 'void free(void*)' called on pointer returned from a mismatched allocation function [-Wmismatched-new-delete]
  844 |     free(data);
      |     ~~~~^~~~~~
../src/Image.cc:834:70: note: returned from 'void* operator new []'(std::size_t)'
  834 |   uint8_t *data = new uint8_t[naturalWidth * naturalHeight * channels];

The triggering condition (the second new uint8_t[] returning nullptr after the first succeeds) is unlikely in practice, but the bug is real and the fix is one character.