Make 'rb_get_args()' va_arg passing safer by introducing a termination marker

What can I say. I made a pact with the devil, and paid dearly.
Almost a whole day's worth of debugging, actually. Not again.

If this turns out to be slow we can always optimize the critical
parts (with no variable param count) later, or completely remove it.

binding-mri/binding-util.cpp

@@ -282,10 +282,51 @@ rb_get_args(int argc, VALUE *argv, const char *format, ...)
 		}
 	}
 
+	/* Pop remaining arg pointers off
+	 * the stack to check for RB_ARG_END */
+	format--;
+
+	while ((c = *format++))
+	{
+		switch (c)
+		{
+		case 'o' :
+		case 'S' :
+			va_arg(ap, VALUE*);
+			break;
+
+		case 's' :
+			va_arg(ap, const char**);
+			va_arg(ap, int*);
+			break;
+
+		case 'z' :
+			va_arg(ap, const char**);
+			break;
+
+		case 'f' :
+			va_arg(ap, double*);
+			break;
+
+		case 'i' :
+			va_arg(ap, int*);
+			break;
+
+		case 'b' :
+			va_arg(ap, bool*);
+			break;
+		}
+	}
+
 	// FIXME print num of needed args vs provided
 	if (!c && argc > argI)
 		rb_raise(rb_eArgError, "wrong number of arguments");
 
+	/* Verify correct termination */
+	void *argEnd = va_arg(ap, void*);
+	Q_UNUSED(argEnd);
+	Q_ASSERT(argEnd == RB_ARG_END);
+
 	va_end(ap);
 
 	return argI;