fix integer overflow in pwg_scan_measurement

[tanjiroK-coder]

1. the digit loop in pwg_scan_measurement accumulates into an int, so a name with ten or more digits wraps: pwgMediaForPWG("custom_max_9999999999x9999999999mm") gives width and length of -727380068.
2. value * numer overflows on its own for much shorter names since numer is up to 100000 for metres: custom_max_1000000x1000000in gives -1754967296.

Both accumulators are long long now and the return saturates at INT_MAX, so valid names decode exactly as before. The size name is remote input, it comes in on media-supported/media-ready and reaches here via cupsCheckDestSupported and cupsGetDestMediaByName, where a negative width then defeats the custom-size range check. Turned up running -fsanitize=undefined over the media name parsers, which fires at pwg-media.c:1065 and :1086; the two testpwg cases fail on master and pass with the change.

Assisted-by: Claude Code:claude-opus-5

[michaelrsweet]

long long isn't universally supported.

Since the maximum value used in IPP is 2^31-1 hundredths of millimeters, I think we can safely just cap the integer portion of the measurement at 10000000 (10km or 157.8mi) and error out for larger values.

[michaelrsweet]

I ended up using 100000 as the maximum value since 2540 * 1000000 is just past the 2^31-1 limit:

[master 6849754] Add limits to PWG media dimension scaning (Issue #176)

[master a922dc0] Drop limit to 100000 (Issue #176)