strv: use realloc_multiply() to check for multiplication overflow

This could overflow on 32bit, where size_t is the same as unsigned.

src/shared/strv.c

@@ -392,7 +392,7 @@ int strv_push(char ***l, char *value) {
         if (m < n)
                 return -ENOMEM;
 
-        c = realloc(*l, sizeof(char*) * (size_t) m);
+        c = realloc_multiply(*l, sizeof(char*), m);
         if (!c)
                 return -ENOMEM;