patch 9.1.0687: Makefile may not install desktop files

Problem:  Makefile may not install desktop files
Solution: Check for "$(DESTDIR)$(DATADIR)" instead of just "$DESTDIR",
          which is usually not defined, add uninstall rules for the
          icons and the desktop files

closes: #15528
fixes: #15546

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 0aa9683..72cce65 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    687,
+/**/
     686,
 /**/
     685,