source/fitz/load-jpeg.c: fixed detection of out-of-range when converting float to int.
source/fitz/load-jpeg.c: fixed detection of out-of-range when converting float to int.

Clang was warning that "implicit conversion from 'int' to 'float' changes
value from 2147483647 to 2147483648 [-Wimplicit-int-float-conversion]". We
could end up overflowing when converting some float values just below INT_MAX
(e.g. 2147483648.0 => -2147483648).

The fix is to do a round-trip conversion and check the value has changed by
less than 1.

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