Reduce lexer's memory consumption

src/libruntime/jerry-libc.c

@@ -211,7 +211,11 @@ __strncpy(char *dest, const char *src, size_t n)
   size_t i;
 
   for (i = 0; i < n; i++)
-    dest[i] = src[i];
+    {
+      dest[i] = src[i];
+      if (src[i] == '\0')
+        break;
+    }
 
   return dest;
 }