map: another fix + test

vlib/builtin/map.v

@@ -57,6 +57,7 @@ fn (m mut map) insert(n mut mapnode, key string, val voidptr) {
 		C.memcpy(n.val, val, m.element_size)
 		if n.is_empty {
 			m.size++
+			n.is_empty = false
 		}
 		return
 	}

vlib/builtin/map_test.v

@@ -189,3 +189,19 @@ fn test_ref() {
 
 }
 */
+
+fn test_delete_size() {
+    arr := ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
+    mut m := map[string]int
+    for _ in 0..10 {
+        for i in 0..10 {
+            m[arr[i]] = i
+        }
+        assert(m.size == 10)
+        println(m.size)
+        for i in 0..10 {
+            m.delete(arr[i])
+        }
+    }
+}
+