patch 8.1.1239: key with byte sequence containing CSI does not work

Problem:    Key with byte sequence containing CSI does not work.
Solution:   Do not recognize CSI as special unless the GUI is active. (Ken
            Takata, closes #4318)
diff --git a/src/getchar.c b/src/getchar.c
index 2dc5e58..a1ffced 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1604,7 +1604,7 @@
 	    // Get two extra bytes for special keys
 	    if (c == K_SPECIAL
 #ifdef FEAT_GUI
-		    || c == CSI
+		    || (gui.in_use && c == CSI)
 #endif
 	       )
 	    {
@@ -1659,19 +1659,23 @@
 		}
 #endif
 #ifdef FEAT_GUI
-		// Handle focus event here, so that the caller doesn't need to
-		// know about it.  Return K_IGNORE so that we loop once (needed
-		// if 'lazyredraw' is set).
-		if (c == K_FOCUSGAINED || c == K_FOCUSLOST)
+		if (gui.in_use)
 		{
-		    ui_focus_change(c == K_FOCUSGAINED);
-		    c = K_IGNORE;
-		}
+		    // Handle focus event here, so that the caller doesn't
+		    // need to know about it.  Return K_IGNORE so that we loop
+		    // once (needed if 'lazyredraw' is set).
+		    if (c == K_FOCUSGAINED || c == K_FOCUSLOST)
+		    {
+			ui_focus_change(c == K_FOCUSGAINED);
+			c = K_IGNORE;
+		    }
 
-		// Translate K_CSI to CSI.  The special key is only used to
-		// avoid it being recognized as the start of a special key.
-		if (c == K_CSI)
-		    c = CSI;
+		    // Translate K_CSI to CSI.  The special key is only used
+		    // to avoid it being recognized as the start of a special
+		    // key.
+		    if (c == K_CSI)
+			c = CSI;
+		}
 #endif
 	    }
 	    // a keypad or special function key was not mapped, use it like
@@ -1749,7 +1753,7 @@
 		    buf[i] = vgetorpeek(TRUE);
 		    if (buf[i] == K_SPECIAL
 #ifdef FEAT_GUI
-			    || buf[i] == CSI
+			    || (gui.in_use && buf[i] == CSI)
 #endif
 			    )
 		    {