Update `khash.h` to pull request 42

https://github.com/attractivechaos/klib/pull/42/files introduces
`kreallocarray`.  Hook that up as our `git__reallocarray`.

src/khash.h

@@ -177,6 +177,9 @@ typedef khint_t khiter_t;
 #ifndef krealloc
 #define krealloc(P,Z) realloc(P,Z)
 #endif
+#ifndef kreallocarray
+#define kreallocarray(P,N,Z) ((SIZE_MAX - N < Z) ? NULL : krealloc(P, (N*Z)))
+#endif
 #ifndef kfree
 #define kfree(P) free(P)
 #endif
@@ -242,15 +245,15 @@ static const double __ac_HASH_UPPER = 0.77;
 			if (new_n_buckets < 4) new_n_buckets = 4;					\
 			if (h->size >= (khint_t)(new_n_buckets * __ac_HASH_UPPER + 0.5)) j = 0;	/* requested size is too small */ \
 			else { /* hash table size to be changed (shrink or expand); rehash */ \
-				new_flags = (khint32_t*)kmalloc(__ac_fsize(new_n_buckets) * sizeof(khint32_t));	\
+				new_flags = (khint32_t*)kreallocarray(NULL, __ac_fsize(new_n_buckets), sizeof(khint32_t)); \
 				if (!new_flags) return -1;								\
 				memset(new_flags, 0xaa, __ac_fsize(new_n_buckets) * sizeof(khint32_t)); \
 				if (h->n_buckets < new_n_buckets) {	/* expand */		\
-					khkey_t *new_keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
+					khkey_t *new_keys = (khkey_t*)kreallocarray((void *)h->keys, new_n_buckets, sizeof(khkey_t)); \
 					if (!new_keys) { kfree(new_flags); return -1; }		\
 					h->keys = new_keys;									\
 					if (kh_is_map) {									\
-						khval_t *new_vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
+						khval_t *new_vals = (khval_t*)kreallocarray((void *)h->vals, new_n_buckets, sizeof(khval_t)); \
 						if (!new_vals) { kfree(new_flags); return -1; }	\
 						h->vals = new_vals;								\
 					}													\
@@ -285,8 +288,8 @@ static const double __ac_HASH_UPPER = 0.77;
 				}														\
 			}															\
 			if (h->n_buckets > new_n_buckets) { /* shrink the hash table */ \
-				h->keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
-				if (kh_is_map) h->vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
+				h->keys = (khkey_t*)kreallocarray((void *)h->keys, new_n_buckets, sizeof(khkey_t)); \
+				if (kh_is_map) h->vals = (khval_t*)kreallocarray((void *)h->vals, new_n_buckets, sizeof(khval_t)); \
 			}															\
 			kfree(h->flags); /* free the working space */				\
 			h->flags = new_flags;										\

src/offmap.h

@@ -13,6 +13,7 @@
 #define kmalloc git__malloc
 #define kcalloc git__calloc
 #define krealloc git__realloc
+#define kreallocarray git__reallocarray
 #define kfree git__free
 #include "khash.h"
 

src/oidmap.h

@@ -13,6 +13,7 @@
 #define kmalloc git__malloc
 #define kcalloc git__calloc
 #define krealloc git__realloc
+#define kreallocarray git__reallocarray
 #define kfree git__free
 #include "khash.h"
 

src/strmap.h

@@ -12,6 +12,7 @@
 #define kmalloc git__malloc
 #define kcalloc git__calloc
 #define krealloc git__realloc
+#define kreallocarray git__reallocarray
 #define kfree git__free
 #include "khash.h"