Added joystick API error checks for shared and Linux code.

src/joystick.c

@@ -47,6 +47,12 @@ GLFWAPI int glfwGetJoystickParam(int joy, int param)
         return 0;
     }
 
+    if (joy < 0 || joy > GLFW_JOYSTICK_LAST)
+    {
+        _glfwSetError(GLFW_INVALID_ENUM, NULL);
+        return 0;
+    }
+
     return _glfwPlatformGetJoystickParam(joy, param);
 }
 
@@ -65,6 +71,18 @@ GLFWAPI int glfwGetJoystickPos(int joy, float* pos, int numaxes)
         return 0;
     }
 
+    if (joy < 0 || joy > GLFW_JOYSTICK_LAST)
+    {
+        _glfwSetError(GLFW_INVALID_ENUM, NULL);
+        return 0;
+    }
+
+    if (pos == NULL || numaxes < 0)
+    {
+        _glfwSetError(GLFW_INVALID_VALUE, NULL);
+        return 0;
+    }
+
     // Clear positions
     for (i = 0;  i < numaxes;  i++)
         pos[i] = 0.0f;
@@ -89,6 +107,18 @@ GLFWAPI int glfwGetJoystickButtons(int joy,
         return 0;
     }
 
+    if (joy < 0 || joy > GLFW_JOYSTICK_LAST)
+    {
+        _glfwSetError(GLFW_INVALID_ENUM, NULL);
+        return 0;
+    }
+
+    if (buttons == NULL || numbuttons < 0)
+    {
+        _glfwSetError(GLFW_INVALID_VALUE, NULL);
+        return 0;
+    }
+
     // Clear button states
     for (i = 0;  i < numbuttons;  i++)
         buttons[i] = GLFW_RELEASE;

src/x11_joystick.c

@@ -236,7 +236,7 @@ int _glfwPlatformGetJoystickParam(int joy, int param)
             return _glfwLibrary.X11.joystick[joy].numButtons;
 
         default:
-            break;
+            _glfwSetError(GLFW_INVALID_ENUM, NULL);
     }
 
     return 0;