patch 9.1.1615: diff format erroneously detected

Problem:  diff format erroneously detected
          (Tomáš Janoušek)
Solution: Make the regex to detect normal diff format a bit stricter,
          while at it, fix wrong test content from patch v9.1.1606

fixes: #17946

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1615,
 /**/
     1614,
 /**/