patch 9.1.1137: ins_str() is inefficient by calling STRLEN()

Problem:  ins_str() is inefficient by calling STRLLEN()
Solution: refactor ins_str() to take a length argument
          and let all callers provide the correct length
          when calling ins_str() (John Marriott)

closes: #16711

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/indent.c b/src/indent.c
index e7de005..6951cfc 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1429,11 +1429,13 @@
 	    ptr = alloc(i + 1);
 	    if (ptr != NULL)
 	    {
+		size_t ptrlen;
 		new_cursor_col += i;
 		ptr[i] = NUL;
+		ptrlen = i;
 		while (--i >= 0)
 		    ptr[i] = ' ';
-		ins_str(ptr);
+		ins_str(ptr, ptrlen);
 		vim_free(ptr);
 	    }
 	}