perf script report: Fix SEGFAULT when using DWARF mode

When running perf script report with a Python script and a callgraph in
DWARF mode, intr_regs->regs can be 0 and therefore crashing the regs_map
function.

Added a check for this condition (same check as in builtin-script.c:595).

Signed-off-by: Andreas Gerstmayr <[email protected]>
Tested-by: Kim Phillips <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt (VMware) <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/util/scripting-engines/trace-event-python.c

@@ -694,6 +694,9 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
 
 	bf[0] = 0;
 
+	if (!regs || !regs->regs)
+		return 0;
+
 	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
 		u64 val = regs->regs[i++];