patch 9.0.2150: Using int for errbuflen in option funcs

Problem:  Using int for errbuflen in option funcs
Solution: Use size_t for errbuflen in string option functions

Use size_t for errbuflen in string option functions

This started as size_t to int warning on Windows in
do_set_option_string().  Other option setting functions are using size_t
for errbuflen so I changed the type in the argument list and then chased
further compiler warnings into the string option functions in
optionstr.c changing ints to size_t as I went.

I also changed the type of os_errbuflen in optset_T to size_t and
updated related argument lists in optionstr.c, as well as updating
set_string_option() to also use size_t for errbuflen for consistency
with other string option setting functions.

closes: #13628

Signed-off-by: Mike Williams <mikew@globalgraphics.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/structs.h

@@ -4969,7 +4969,7 @@ typedef struct
     // message (when it is not NULL).
     char	*os_errbuf;
     // length of the error buffer
-    int		os_errbuflen;
+    size_t	os_errbuflen;
 } optset_T;
 
 /*