patch 8.0.1435: memory leak in test_arabic

Problem:    Memory leak in test_arabic.
Solution:   Free the from and to parts. (Christian Brabandt, closes #2569)
diff --git a/src/buffer.c b/src/buffer.c
index eeba530..ecd8f4e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2212,6 +2212,7 @@
     clear_string_option(&buf->b_p_isk);
 #ifdef FEAT_KEYMAP
     clear_string_option(&buf->b_p_keymap);
+    keymap_clear(&buf->b_kmap_ga);
     ga_clear(&buf->b_kmap_ga);
 #endif
 #ifdef FEAT_COMMENTS