patch 8.1.0702: ":sign place" only uses the current buffer

Problem:    ":sign place" only uses the current buffer.
Solution:   List signs for all buffers when there is no buffer argument.
            Fix error message for invalid buffer name in sign_place().
            (Yegappan Lakshmanan, closes #3774)

src/version.c

@@ -799,6 +799,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    702,
 /**/
     701,
 /**/