This patch fixes PR16508, which is about MI "-trace-find frame-number 0"
behaves differently from CLI "tfind 0". In CLI, we check both
status->running and status->filename, but in MI, we only check
status->running, which looks wrong to me. This patch moves the code
of checking to a new function check_trace_running, and use it in
both CLI and MI.
This patch also adds a test case pr16508.exp, which fails without this
fix, and passes with the fix applied.
FAIL: gdb.trace/pr16508.exp: interpreter-exec mi "-trace-find frame-number 0"