Use or_else in the core library when it makes sense

core/os/os2/errors.odin

@@ -57,11 +57,8 @@ link_error_delete :: proc(lerr: Maybe(Link_Error)) {
 
 
 is_platform_error :: proc(ferr: Error) -> (err: i32, ok: bool) {
-	v: Platform_Error;
-	if v, ok = ferr.(Platform_Error); ok {
-		err = v.err;
-	}
-	return;
+	v := or_else(ferr.(Platform_Error), {});
+	return v.err, v.err != 0;
 }
 
 

core/os/os2/file_stream.odin

@@ -13,11 +13,7 @@ error_to_io_error :: proc(ferr: Error) -> io.Error {
 	if ferr == nil {
 		return .None;
 	}
-	err, ok := ferr.(io.Error);
-	if !ok {
-		err = .Unknown;
-	}
-	return err;
+	return or_else(ferr.(io.Error), .Unknown);
 }