process.gdb-remote crashes Part 3

In source/API/SBFrame.cpp, it is assumed that GetRegisterContext() is not null, and there is no way in the public API to check it either.
With the gdb plugin, sometimes the Frame is valid, but the register context is not, leading to a crash on GetSP for example.
There should probably either be a way to check the validity from the outside, or SBFrame::IsValid should only return true if GetRegisterContext works
(the frame is unusable anyway, if it doesn't)

Again this is probably due to your program running when you are making the API calls. We need to make sure we can't access stopped program state when the program is running.