[rtextures][rlgl] Fix pixel data size regressions

[GideonSerf]

Problem

Recent pixel-size hardening added 64-bit variables to safely check image data sizes before converting them to int. Some multiplication operands remain int, so the intermediate calculation may still occur at 32-bit width before assignment.

Explicitly promoting the first operand ensures the calculation consistently uses 64-bit arithmetic across compilers.

ImageRotate() used the total destination image size as its per-pixel stride, causing out-of-bounds access for images larger than one pixel.

Fix

• Promote pixel-size multiplication operands before evaluation in both GetPixelDataSize() and rlGetPixelDataSize().
• Keep ImageRotate() allocation size and per-pixel stride as separate values.

Validation

• Reproduced the ImageRotate() overflow with MSVC AddressSanitizer.
• Verified large valid and over-limit pixel-size calculations.
• Verified zero-degree RGBA8 image rotation preserves dimensions and data.
• Built raylib and all examples with MSVC x64 Release.

[raysan5]

@GideonSerf Oh! Thanks for the review!

[GideonSerf]

@raysan5 No problem 😊!