patch 9.0.2114: overflow detection not accurate when adding digits

Problem:  overflow detection not accurate when adding digits
Solution: Use a helper function

Use a helper function to better detect overflows before adding integer
digits to a long or an integer variable respectively. Signal the
overflow to the caller function.

closes: #13539

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Michael Henry <vim@drmikehenry.com>
Signed-off-by: Ernie Rael <errael@raelity.com>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2114,
 /**/
     2113,
 /**/