tools/thermal: tmon: fix for segfault

Fixes a segfault occurring when e.g. <TAB> is pressed multiple times in the
ncurses tmon application. The segfault is caused by incrementing
cur_thermal_record in the main function without checking if it's value reached
NR_THERMAL_RECORD immediately. Since the boundary check only occurred in
update_thermal_data a race condition existed, which lead to an attempted read
beyond the last element of the trec array.

The fix was implemented by moving the cur_thermal_record incrementation to the
update_thermal_data function using a temporary variable on which the boundary
condition is checked before updating cur_thread_record, so that the variable is
never incremented beyond the trec array's boundary.

It seems the segfault does not occur on every machine: On a HP EliteBook G4 the
segfault happens, while it does not happen on a Thinkpad T540p.

Signed-off-by: Frank Asseg <frank.asseg@objecthunter.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>