Null dereference within DbgEngAdapter::ReadMemory

[sentry]

Sentry Issue: BINARYNINJA-5Z

EXCEPTION_ACCESS_VIOLATION_READ / 0x0: Fatal Error: EXCEPTION_ACCESS_VIOLATION_READ / 0x0
  File "dbgengadapter.cpp", line 2182, in BinaryNinjaDebugger::DbgEngAdapter::ReadMemory
  File "debuggercontroller.cpp", line 65, in BinaryNinjaDebugger::DebuggerController::AddBreakpoint
  File "debuggerstate.cpp", line 713, in BinaryNinjaDebugger::DebuggerBreakpoints::ContainsAbsolute
  File "viewframe.cpp", line 1479, in View::getViewFromWidget
  File "uicontext.cpp", line 762, in UIContext::contextForWidget
...
(35 additional frame(s) were not displayed)

@bdash says:

The crash occurs when DbgEngAdapter::ReadMemory dereferences m_debugDataSpaces when it is null. I don't see anything that guarantees that ReadMemory cannot be be called when m_debugDataSpaces is null, so presumably a null check should be added (ditto within WriteMemory).