Fixed crash on earlier liblldb versions, and changed a couple debug key bindings from n (used for new file and directory) to h

src/debug.cc

@@ -262,7 +262,8 @@ std::vector<Debug::Frame> Debug::get_backtrace() {
     for(uint32_t c_f=0;c_f<thread.GetNumFrames();c_f++) {
       Frame backtrace_frame;
       auto frame=thread.GetFrameAtIndex(c_f);
-      backtrace_frame.function_name=frame.GetFunctionName();
+      if(frame.GetFunction().IsValid())
+        backtrace_frame.function_name=frame.GetFunctionName();
       auto line_entry=frame.GetLineEntry();
       if(line_entry.IsValid()) {
         lldb::SBStream stream;

src/files.h

@@ -103,10 +103,10 @@ const std::string configjson =
 "        \"debug_start_continue\": \"<primary>y\",\n"
 "        \"debug_stop\": \"<primary><shift>y\",\n"
 "        \"debug_kill\": \"<primary><shift>k\",\n"
-"        \"debug_step_over\": \"<primary>n\",\n"
+"        \"debug_step_over\": \"<primary>h\",\n"
 "        \"debug_step_into\": \"<primary>t\",\n"
 "        \"debug_step_out\": \"<primary><shift>t\",\n"
-"        \"debug_backtrace\": \"<primary><shift>n\",\n"
+"        \"debug_backtrace\": \"<primary><shift>h\",\n"
 "        \"debug_run_command\": \"<alt><shift>Return\",\n"
 "        \"debug_toggle_breakpoint\": \"<primary>b\",\n"
 "        \"debug_goto_stop\": \"<primary><shift>l\",\n"