Fix end-of-string calculation

In keys_fill_missing() a pointer is walked through a string of
space-separated character names, but misses the string-terminating null
character.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/keys.c

@@ -731,7 +731,7 @@ void keys_fill_missing(void)
 							  "\"%s\" was already assigned!"),
 							 keydef[i].label,
 							 key_ch);
-					p += strlen(key_ch) + 1;
+					p += strlen(key_ch);
 				} else {
 					break;
 				}