Fix return value on error for glfwGetKeyScancode

The documentation says it should be -1, not zero.

(cherry picked from commit 8c5471d6cd)

README.md

@@ -123,6 +123,7 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
+ - Bugfix: `glfwGetKeyScancode` returned `0` on error when initialized instead of `-1`
  - [Win32] Fix pkg-config for dynamic library on Windows (#2386, #2420)
  - [Win32] Bugfix: `glfwWaitEventsTimeout` did not return for some sent messages (#2408)
  - [Wayland] Added improved fallback window decorations via libdecor (#1639,#1693)

src/input.c

@@ -636,7 +636,7 @@ GLFWAPI int glfwGetKeyScancode(int key)
     if (key < GLFW_KEY_SPACE || key > GLFW_KEY_LAST)
     {
         _glfwInputError(GLFW_INVALID_ENUM, "Invalid key %i", key);
-        return GLFW_RELEASE;
+        return -1;
     }
 
     return _glfwPlatformGetKeyScancode(key);