Use macros to improve safety loading callbacks

Just a minor fix mostly because I noticed that I kept accidentally
forgetting to add checks to the code properly.  This is one of those
cases where macros come in useful, as macros can automate the process
and help prevent these mistakes from happening by accident.

libobs/obs-data.h

@@ -32,6 +32,14 @@
 #include "obs-service.h"
 #include "obs-encoder.h"
 
+#define LOAD_MODULE_SUBFUNC(name, required) \
+	do { \
+		info->name = load_module_subfunc(module, module_name, \
+				id, #name, required); \
+		if (required && !info->name) \
+			return false; \
+	} while (false)
+
 #define NUM_TEXTURES 2
 
 struct obs_display {