Fixed undefined behavior of isgraph when passing integer

[nmoinvaz]

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/isgraph-iswgraph-isgraph-l-iswgraph-l?view=msvc-160

The behavior of isgraph and _isgraph_l is undefined if c is not EOF or in the range 0 through 0xFF, inclusive. When a debug CRT library is used and c is not one of these values, the functions raise an assertion.

[codecov]

Codecov Report

Merging #1036 (a4fcad1) into develop (e128537) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1036   +/-   ##
========================================
  Coverage    78.32%   78.32%           
========================================
  Files           85       85           
  Lines         8730     8730           
  Branches      1392     1395    +3     
========================================
  Hits          6838     6838           
  Misses        1357     1357           
  Partials       535      535           

Flag	Coverage Δ
macos_clang	68.06% <ø> (ø)
macos_gcc	66.70% <ø> (ø)
ubuntu_clang	73.36% <ø> (ø)
ubuntu_clang_debug	73.68% <100.00%> (ø)
ubuntu_clang_inflate_allow_invalid_dist	73.11% <ø> (ø)
ubuntu_clang_inflate_strict	73.35% <ø> (ø)
ubuntu_clang_mmap	73.34% <ø> (ø)
ubuntu_clang_msan	73.36% <ø> (ø)
ubuntu_clang_pigz	34.08% <ø> (ø)
ubuntu_clang_pigz_no_optim	38.18% <ø> (ø)
ubuntu_clang_pigz_no_threads	33.62% <ø> (ø)
ubuntu_clang_reduced_mem	73.63% <ø> (ø)
ubuntu_gcc	72.83% <ø> (ø)
ubuntu_gcc_aarch64	74.74% <ø> (ø)
ubuntu_gcc_aarch64_compat_no_opt	72.38% <ø> (ø)
ubuntu_gcc_aarch64_no_acle	74.02% <ø> (ø)
ubuntu_gcc_aarch64_no_neon	74.29% <ø> (ø)
ubuntu_gcc_armhf	74.73% <ø> (ø)
ubuntu_gcc_armhf_compat_no_opt	72.35% <ø> (ø)
ubuntu_gcc_armhf_no_acle	74.99% <ø> (ø)
ubuntu_gcc_armhf_no_neon	75.23% <ø> (ø)
ubuntu_gcc_armsf	74.74% <ø> (ø)
ubuntu_gcc_armsf_compat_no_opt	72.35% <ø> (ø)
ubuntu_gcc_compat_no_opt	73.49% <ø> (ø)
ubuntu_gcc_mingw_i686	0.00% <ø> (ø)
ubuntu_gcc_mingw_x86_64	0.00% <ø> (ø)
ubuntu_gcc_no_avx2	74.71% <ø> (ø)
ubuntu_gcc_no_pclmulqdq	71.40% <ø> (ø)
ubuntu_gcc_no_sse2	73.81% <ø> (ø)
ubuntu_gcc_no_sse4	71.72% <ø> (ø)
ubuntu_gcc_o3	72.03% <ø> (ø)
ubuntu_gcc_osb	75.85% <100.00%> (ø)
ubuntu_gcc_pigz	34.45% <ø> (+0.02%)	⬆️
ubuntu_gcc_pigz_aarch64	36.15% <ø> (+0.03%)	⬆️
ubuntu_gcc_ppc	72.71% <ø> (ø)
ubuntu_gcc_ppc64	75.61% <ø> (ø)
ubuntu_gcc_ppc64le	74.15% <ø> (ø)
ubuntu_gcc_ppc_no_power8	75.25% <ø> (ø)
ubuntu_gcc_s390x	74.05% <ø> (ø)
ubuntu_gcc_sparc64	76.39% <ø> (ø)
win64_gcc	∅ <ø> (∅)
win64_gcc_compat_no_opt	∅ <ø> (∅)

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Impacted Files	Coverage Δ
trees.c	96.44% <100.00%> (ø)
trees_emit.h	100.00% <100.00%> (ø)

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