limit IDAT decompression size to expected_size

[nevernever69]

Set max_output_size before IDAT decompression, consistent with how zTXt and iCCP chunks are already handled. This prevents large memory allocation when IDAT decompresses to more than expected.

The issue:

• IDAT decompression doesn't set max_output_size (line 5494)
• zTXt and iCCP already set it (lines 4939 and 5130)
• A malformed PNG can cause large allocation before error 91

The fix:

• Copy zlibsettings and set max_output_size = expected_size
• Same pattern already used for zTXt/iCCP

Test result:

• Before: 1KB PNG causes 1MB allocation, then error 91
• After: Early error 109, no large allocation
• Valid PNGs unaffected