perf(image): remove redundant getimagesize() call in JPEG load path

[joshtrichards]

Summary

Remove the second getimagesize() call from the JPEG branch in OC\Image::loadFromFile().

After PR #46342 this second call become redundant. checkImageSize() already calls getimagesize() and returns false when the image data cannot be read, so the JPEG-specific follow-up check is redundant. The image can be passed directly to imagecreatefromjpeg() after the existing guard succeeds.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI