Memmap: Don't show panic alert for 0 length range

IOS::HLE::IOCtlVRequest::Dump sometimes tries to call GetPointerForRange
with an address of 0 and a size of 0. Address 0 is valid, but we were
mistakenly also trying to check that address 3FFFFFFF is valid, which it
isn't.

Fixes https://bugs.dolphin-emu.org/issues/13514.

Source/Core/Core/HW/Memmap.cpp

@@ -409,7 +409,7 @@ u8* MemoryManager::GetPointerForRange(u32 address, size_t size) const
 
   // Check that the beginning and end of the range are valid
   u8* pointer = GetPointer(address);
-  if (!pointer || !GetPointer(address + u32(size) - 1))
+  if (pointer == nullptr || (size != 0 && GetPointer(address + u32(size) - 1) == nullptr))
   {
     // A panic alert has already been raised by GetPointer
     return nullptr;