Add null RegisterContext assertions

This makes these failures slightly more obvious, avoiding the need to
run LLDB under a debugger or rely on a LLDB core.  I encountered these
while bringing up a new OS/arch combination.

llvm-svn: 230236

lldb/source/Target/StackFrameList.cpp

@@ -343,6 +343,7 @@ StackFrameList::GetFramesUpTo(uint32_t end_idx)
                 m_frames.push_back (unwind_frame_sp);
             }
             
+            assert(unwind_frame_sp);
             SymbolContext unwind_sc = unwind_frame_sp->GetSymbolContext (eSymbolContextBlock | eSymbolContextFunction);
             Block *unwind_block = unwind_sc.block;
             if (unwind_block)

lldb/source/Target/ThreadPlan.cpp

@@ -156,6 +156,7 @@ ThreadPlan::WillResume (StateType resume_state, bool current_plan)
         if (log)
         {
             RegisterContext *reg_ctx = m_thread.GetRegisterContext().get();
+            assert (reg_ctx);
             addr_t pc = reg_ctx->GetPC();
             addr_t sp = reg_ctx->GetSP();
             addr_t fp = reg_ctx->GetFP();