Fixed potential uninitialized memory access (thanks Mathieu!)

GetRawInputDeviceList() can return a different number of devices than was allocated.

Fixes https://github.com/libsdl-org/SDL/issues/2759

(cherry picked from commit b9784feb2467dbb4cdc2474aa78098cd4f0b1630)

src/joystick/windows/SDL_rawinputjoystick.c

@@ -988,7 +988,8 @@ static void RAWINPUT_DetectDevices(void)
 
         devices = (PRAWINPUTDEVICELIST)SDL_malloc(sizeof(RAWINPUTDEVICELIST) * device_count);
         if (devices) {
-            if (GetRawInputDeviceList(devices, &device_count, sizeof(RAWINPUTDEVICELIST)) != -1) {
+            device_count = GetRawInputDeviceList(devices, &device_count, sizeof(RAWINPUTDEVICELIST));
+            if (device_count != (UINT)-1) {
                 for (i = 0; i < device_count; ++i) {
                     RAWINPUT_AddDevice(devices[i].hDevice);
                 }

src/joystick/windows/SDL_windows_gaming_input.c

@@ -136,7 +136,8 @@ static SDL_bool SDL_IsXInputDevice(Uint16 vendor, Uint16 product)
         return SDL_FALSE;
     }
 
-    if (GetRawInputDeviceList(raw_devices, &raw_device_count, sizeof(RAWINPUTDEVICELIST)) == -1) {
+    raw_device_count = GetRawInputDeviceList(raw_devices, &raw_device_count, sizeof(RAWINPUTDEVICELIST));
+    if (raw_device_count == (UINT)-1) {
         SDL_free(raw_devices);
         raw_devices = NULL;
         return SDL_FALSE; /* oh well. */

src/joystick/windows/SDL_xinputjoystick.c

@@ -134,7 +134,8 @@ static void GuessXInputDevice(Uint8 userid, Uint16 *pVID, Uint16 *pPID, Uint16 *
         return;
     }
 
-    if (GetRawInputDeviceList(devices, &device_count, sizeof(RAWINPUTDEVICELIST)) == -1) {
+    device_count = GetRawInputDeviceList(devices, &device_count, sizeof(RAWINPUTDEVICELIST));
+    if (device_count == (UINT)-1) {
         SDL_free(devices);
         return; /* oh well. */
     }