patch 9.0.0312: test for cmdheight zero fails

Problem:    Test for cmdheight zero fails.
Solution:   Do not close the messages window for CTRL-C.
diff --git a/src/normal.c b/src/normal.c
index 12b611e..926f504 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -6822,7 +6822,7 @@
     else if (no_reason)
     {
 #ifdef HAS_MESSAGE_WINDOW
-	if (popup_message_win_visible())
+	if (!cap->arg && popup_message_win_visible())
 	    popup_hide_message_win();
 	else
 #endif
diff --git a/src/version.c b/src/version.c
index e6ecb97..61793a9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -708,6 +708,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    312,
+/**/
     311,
 /**/
     310,