HW: Remove calls to GetPointer

Typically when someone uses GetPointer, it's because they want to read
from a range of memory. GetPointer is unsafe to use for this. While it
does check that the passed-in address is valid, it doesn't know the size
of the range that will be accessed, so it can't check that the end
address is valid. The safer alternative GetPointerForRange should be
used instead.

Note that there is still the problem of many callers not checking for
nullptr.

This is part 2 of a series of changes removing the use of GetPointer
throughout the code base. After this, VideoCommon is the one major part
of Dolphin that remains.

Source/Core/Core/PowerPC/GDBStub.cpp

@@ -831,7 +831,7 @@ static void ReadMemory(const Core::CPUThreadGuard& guard)
 
   auto& system = Core::System::GetInstance();
   auto& memory = system.GetMemory();
-  u8* data = memory.GetPointer(addr);
+  u8* data = memory.GetPointerForRange(addr, len);
   Mem2hex(reply, data, len);
   reply[len * 2] = '\0';
   SendReply((char*)reply);
@@ -858,7 +858,7 @@ static void WriteMemory(const Core::CPUThreadGuard& guard)
 
   auto& system = Core::System::GetInstance();
   auto& memory = system.GetMemory();
-  u8* dst = memory.GetPointer(addr);
+  u8* dst = memory.GetPointerForRange(addr, len);
   Hex2mem(dst, s_cmd_bfr + i + 1, len);
   SendReply("OK");
 }