stubs/atom.c: Fix memory leak in __libxfont_internal__MakeAtom
Reported by a static analysis tool:
9. libXfont2-2.0.6/src/stubs/atom.c:179:5:
alloc_fn: Storage is returned from allocation function "malloc".
10. libXfont2-2.0.6/src/stubs/atom.c:179:5:
var_assign: Assigning: "a" = storage returned from
"malloc(24UL + len + 1UL)".
16. libXfont2-2.0.6/src/stubs/atom.c:194:6:
leaked_storage: Variable "a" going out of scope leaks the
storage it points to.
# 192| if ((ResizeHashTable() == FALSE) &&
# 193| ((hashTable == NULL) || (hashUsed == hashSize)))
# 194|-> return None;
# 195| h = hash & hashMask;
# 196| if (hashTable[h]) {
Fixes: 78085e6b ("stubs/atom.c: check for ResizeHashTable failure")