patch 8.2.4828: fix for unmapping simplified key not fully tested

Problem:    Fix for unmapping simplified key not fully tested.
Solution:   Add a test case. (closes #10292)
diff --git a/src/map.c b/src/map.c
index ea7567e..186550a 100644
--- a/src/map.c
+++ b/src/map.c
@@ -726,6 +726,8 @@
 				    mpp = &(mp->m_next);
 				    continue;
 				}
+				// In keyround for simplified keys, don't unmap
+				// a mapping without m_simplified flag.
 				if (keyround1_simplified && !mp->m_simplified)
 				    break;
 				// We reset the indicated mode bits. If nothing