Fix function return value when uninitialized

src/input.c

@@ -721,7 +721,7 @@ GLFWAPI const char* glfwGetKeyName(int key, int scancode)
 
 GLFWAPI int glfwGetKeyScancode(int key)
 {
-    _GLFW_REQUIRE_INIT_OR_RETURN(-1);
+    _GLFW_REQUIRE_INIT_OR_RETURN(0);
 
     if (key < GLFW_KEY_SPACE || key > GLFW_KEY_LAST)
     {