[VIEW] Fix configuration errors when Glew is missing

Glew should be an optional dependency on macOS and Linux but previously
caused configuration errors when missing.

CMakeLists.txt

@@ -590,7 +590,11 @@ ENDIF()
 
 IF (BALL_HAS_VIEW)
 ## TODO: Qt handling!
-	LIST(APPEND VIEW_DEP_LIBRARIES ${GLEW_LIBRARY} ${RTFACT_LIBRARIES})
+	IF(GLEW_FOUND)
+		LIST(APPEND VIEW_DEP_LIBRARIES ${GLEW_LIBRARY})
+	ENDIF()
+
+	LIST(APPEND VIEW_DEP_LIBRARIES ${RTFACT_LIBRARIES})
 
 	SET_TARGET_PROPERTIES(VIEW PROPERTIES
 		SOVERSION "${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}"