Remove unnecessary and extra zero length check in mem functions' macro (#2428)

In macro bh_memcpy_s, bh_memcy_wa and bh_memmove_s, no need to do extra check
for length is zero or not because it was already done inside of the functions called.

core/shared/utils/bh_common.c

@@ -31,6 +31,10 @@ b_memcpy_wa(void *s1, unsigned int s1max, const void *s2, unsigned int n)
     unsigned int *p;
     char *ps;
 
+    if (n == 0) {
+        return 0;
+    }
+
     if (pa > src) {
         pa -= 4;
     }