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)
diff --git a/src/version.c b/src/version.c
index eb7b268..13f7909 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    702,
+/**/
     701,
 /**/
     700,