Fix out-of-range comparison in _XF86BigfontQueryFont

clang complained (correctly):
warning: comparison of constant 768614336404564650 with expression
of type 'CARD32' (aka 'unsigned int') is always true
[-Wtautological-constant-out-of-range-compare]

[While LONG_MAX is correct, since it's used in size_t math, the
 numbers have to be limited to 32-bit range to be usable by 32-bit
 clients, and values beyond that range are far more likely to be
 bugs in the data from the server than valid numbers of characters
 in a font.   -alan- ]

Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Tighten out-of-range comparisons.

[For all of these, LONG_MAX was the correct value to prevent overflows
 for the recent CVEs.   Lowering to INT_MAX catches buggy replies from
 the server that 32-bit clients would reject but 64-bit would accept,
 so we catch bugs sooner, and really, no sane & working server should
 ever report more than 2gb of extension names, font path entries,
 key modifier maps, etc.  -alan- ]

Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>