Fix iOS font weight regression due to boolean coercion

[ptptsw]

Summary:

This PR fixes a regression introduced in version 0.83.1 regarding font weight handling on iOS.

The Issue: In a recent change to font handling logic (likely intended for cleanup), a logic error was introduced using the Elvis operator combined with a boolean comparison.
#54934

// 🐛 Buggy logic in 0.83.1
fontWeight = (fontWeight != 0.0) ?: RCTGetFontWeight(font);

Changelog:

[IOS] [FIXED] - Fix regression where custom fonts with specific weights rendered as Black/ExtraBold due to incorrect boolean coercion

Test Plan:

I verified this fix using a reproduction app with a custom font (e.g., Pretendard) that has multiple weights.

Environment: React Native 0.83.1

Before Fix: The text rendered as UIFontWeightBlack (extremely thick) because fontWeight was coerced to 1.0.

After Fix: The text correctly renders with the intended weight ('Pretendard-SemiBold'/600).

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