patch 9.0.1480: using popup menu may leave text in the command line

Problem:    Using popup menu may leave text in the command line.
Solution:   Clear the command line if the popup menu covered it. (Luuk van
            Baal, closes #12286)
diff --git a/src/popupmenu.c b/src/popupmenu.c
index d713ed4..36d3b99 100644
--- a/src/popupmenu.c
+++ b/src/popupmenu.c
@@ -18,6 +18,7 @@
 static int pum_first = 0;		// index of top item
 
 static int call_update_screen = FALSE;
+static int pum_in_cmdline = FALSE;
 
 static int pum_height;			// nr of displayed pum items
 static int pum_width;			// width of displayed pum items
@@ -1067,6 +1068,11 @@
     pum_array = NULL;
     redraw_all_later(UPD_NOT_VALID);
     redraw_tabline = TRUE;
+    if (pum_in_cmdline)
+    {
+	clear_cmdline = TRUE;
+	pum_in_cmdline = FALSE;
+    }
     status_redraw_all();
 #if defined(FEAT_PROP_POPUP) && defined(FEAT_QUICKFIX)
     // hide any popup info window
@@ -1193,6 +1199,8 @@
 	pum_row = mouse_row + 1;
 	if (pum_height > Rows - pum_row)
 	    pum_height = Rows - pum_row;
+	if (pum_row + pum_height > cmdline_row)
+	    pum_in_cmdline = TRUE;
     }
     else
     {