[rcore] Add gamepad >= 0 lower-bound guard to six sibling functions (#5938)

Commit 3edfe19 added a `gamepad >= 0` lower-bound check to
GetGamepadAxisCount() and GetGamepadName(), but six sibling functions
were left with only the upper-bound check (`gamepad < MAX_GAMEPADS`).
A negative signed int passes that check and triggers out-of-bounds
access on CORE.Input.Gamepad.ready[gamepad] and related arrays (UB in C).

Apply the same `(gamepad >= 0) &&` guard added in 3edfe19 to:
- IsGamepadAvailable
- IsGamepadButtonPressed
- IsGamepadButtonDown
- IsGamepadButtonReleased
- IsGamepadButtonUp
- GetGamepadAxisMovement

Author: mahirhir

src/rcore.c

@@ -3926,7 +3926,7 @@ bool IsGamepadAvailable(int gamepad)
 {
     bool result = false;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad]) result = true;
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad]) result = true;
 
     return result;
 }
@@ -3946,7 +3946,7 @@ bool IsGamepadButtonPressed(int gamepad, int button)
 {
     bool pressed = false;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
     {
         if ((CORE.Input.Gamepad.previousButtonState[gamepad][button] == 0) && (CORE.Input.Gamepad.currentButtonState[gamepad][button] == 1)) pressed = true;
     }
@@ -3959,7 +3959,7 @@ bool IsGamepadButtonDown(int gamepad, int button)
 {
     bool down = false;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
     {
         if (CORE.Input.Gamepad.currentButtonState[gamepad][button] == 1) down = true;
     }
@@ -3972,7 +3972,7 @@ bool IsGamepadButtonReleased(int gamepad, int button)
 {
     bool released = false;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
     {
         if ((CORE.Input.Gamepad.previousButtonState[gamepad][button] == 1) && (CORE.Input.Gamepad.currentButtonState[gamepad][button] == 0)) released = true;
     }
@@ -3985,7 +3985,7 @@ bool IsGamepadButtonUp(int gamepad, int button)
 {
     bool up = false;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (button < MAX_GAMEPAD_BUTTONS))
     {
         if (CORE.Input.Gamepad.currentButtonState[gamepad][button] == 0) up = true;
     }
@@ -4015,7 +4015,7 @@ float GetGamepadAxisMovement(int gamepad, int axis)
 {
     float value = ((axis == GAMEPAD_AXIS_LEFT_TRIGGER) || (axis == GAMEPAD_AXIS_RIGHT_TRIGGER))? -1.0f : 0.0f;
 
-    if ((gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (axis < MAX_GAMEPAD_AXES))
+    if ((gamepad >= 0) && (gamepad < MAX_GAMEPADS) && CORE.Input.Gamepad.ready[gamepad] && (axis < MAX_GAMEPAD_AXES))
     {
         float movement = (value < 0.0f)? CORE.Input.Gamepad.axisState[gamepad][axis] : fabsf(CORE.Input.Gamepad.axisState[gamepad][axis]);