patch 9.1.0274: MS-Windows: a few compiler warnings

Problem:  MS-Windows: a few compiler warnings
Solution: Change variable types to resolve compiler warnings
          (Mike Williams)

Windows compiles were reporting a few size_t to signed integer
conversion warnings that can be resolved by changing the variable
declarations to be size_t to start with.

closes: #14429

Signed-off-by: Mike Williams <mrmrdubya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ops.c b/src/ops.c
index dbdf119..0ab0d00 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -1593,12 +1593,12 @@
 
     if (oap->block_mode)
     {
-	long			ins_len;
+	size_t			ins_len;
 	char_u			*firstline, *ins_text;
 	struct block_def	bd2;
 	int			did_indent = FALSE;
 	size_t			len;
-	int			add;
+	size_t			add;
 	// offset when cursor was moved in insert mode
 	int			offset = 0;
 
@@ -1703,7 +1703,7 @@
 		    return;
 	    }
 	}
-	if ((size_t)add > len)
+	if (add > len)
 	    add = len;  // short line, point to the NUL
 	firstline += add;
 	len -= add;