feefrac_mul_div: Integer-overflow in FeeFrac::Div #32294

https://issues.oss-fuzz.com/issues/411172125:

echo '//v////7/////f////////8=' | base64 --decode > /tmp/dat

UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" FUZZ=feefrac_mul_div  ./bld-cmake/bin/fuzz /tmp/dat

src/util/feefrac.h:99:21: runtime error: signed integer overflow: 9223372036854775807 + 1 cannot be represented in type 'int64_t' (aka 'long')

See #32300.