patch 9.0.1199: crash when using kitty and using a mapping with <Esc>

Problem:    Crash when using kitty and using a mapping with <Esc>.
Solution:   Do not try setting did_simplify when it is NULL. (closes #11817)
diff --git a/src/term.c b/src/term.c
index 0b902c9..ff31b1e 100644
--- a/src/term.c
+++ b/src/term.c
@@ -6636,8 +6636,10 @@
 		}
 	    }
 #endif
-	    slen = trans_special(&src, result + dlen, FSK_KEYCODE
-			  | ((flags & REPTERM_NO_SIMPLIFY) ? 0 : FSK_SIMPLIFY),
+	    int fsk_flags = FSK_KEYCODE
+			| ((flags & REPTERM_NO_SIMPLIFY) ? 0 : FSK_SIMPLIFY)
+			| ((flags & REPTERM_FROM_PART) ? FSK_FROM_PART : 0);
+	    slen = trans_special(&src, result + dlen, fsk_flags,
 							   TRUE, did_simplify);
 	    if (slen > 0)
 	    {