Linux/MacOSX: Don't always ignore /dev/random failure by making sure that it has returned random bytes successfully at least once during the lifetime of RandomNumberGenerator

src/Core/RandomNumberGenerator.h

@@ -55,6 +55,7 @@ namespace VeraCrypt
 		static bool Running;
 		static size_t WriteOffset;
 		static struct rand_data *JitterRngCtx;
+		static bool DevRandomSucceeded;
 	};
 }