patch 9.1.1691: over-allocation in ga_concat_strings()

Problem:  over-allocation in ga_concat_strings()
Solution: Fix ga_concat_strings() and only allocate n-1 separator length
          bytes (Damien Lejay).

ga_concat_strings() was adding the separator length for every item,
including the last one. Only (n - 1) separators are actually used.
This caused harmless but unnecessary overallocation.

closes: #18112

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/alloc.c

@@ -770,7 +770,10 @@ ga_concat_strings(garray_T *gap, char *sep)
     char_u	*p;
 
     for (i = 0; i < gap->ga_len; ++i)
-	len += (int)STRLEN(((char_u **)(gap->ga_data))[i]) + sep_len;
+	len += (int)STRLEN(((char_u **)(gap->ga_data))[i]);
+
+    if (gap->ga_len > 1)
+	len += (gap->ga_len - 1) * sep_len;
 
     s = alloc(len + 1);
     if (s == NULL)

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1691,
 /**/
     1690,
 /**/