string-util: introduce explicit_zero_safe()

The only real difference is that this wrapper can deal with NULL
pointer arguments, but only if the length is also zero.

CID 1396277

src/basic/string-util.h

@@ -198,8 +198,15 @@ static inline void *memmem_safe(const void *haystack, size_t haystacklen, const
         return memmem(haystack, haystacklen, needle, needlelen);
 }
 
-#if !HAVE_EXPLICIT_BZERO
-void explicit_bzero(void *p, size_t l);
+#if HAVE_EXPLICIT_BZERO
+static inline void* explicit_bzero_safe(void *p, size_t l) {
+        if (l > 0)
+                explicit_bzero(p, l);
+
+        return p;
+}
+#else
+void explicit_bzero_safe(void *p, size_t l);
 #endif
 
 char *string_erase(char *x);