cleanup(libsinsp): update g_invalidchar for windows

Signed-off-by: Luca Guerra <[email protected]>

userspace/libsinsp/utils.h

@@ -175,7 +175,7 @@ struct g_invalidchar
 	{
 		// Exclude all non-printable characters and control characters while
 		// including a wide range of languages (emojis, cyrillic, chinese etc)
-		return !(isprint((unsigned)c));
+		return (c < -1 || c > 255 || !(isprint((unsigned)c)));
 	}
 };