lib: fix backtraces broken by 837d16c...

837d16c ("*: use array_size() helper macro") accidentally changed one of
the expressions in the backtrace code, which afterwards read:

zlog_backtrace_sigsafe():
  if (((size = backtrace(array,array_size(array)) <= 0) ||

which boils down to: (size = backtrace(...)  <= 0).  The braces were
intended to go:      (size = backtrace(...)) <= 0.

All in all, this makes a nice textbook example of the original author
being too clever (trying to save a single line by pulling the assignment
into the condition) and the next person touching the code tripping over
it...

This code occurs another time in zlog_backtrace() where it is actually
correct.  Pulling out the assignment nonetheless.  Also, new test
program.

Cc: Andrew J. Schorr <ajschorr@alumni.princeton.edu>
Cc: Balaji.G <balajig81@gmail.com>
Cc: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 9260a90..5e631d6 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -24,13 +24,14 @@
 TESTS_BGPD =
 endif
 
-check_PROGRAMS = testsig testbuffer testmemory heavy heavywq heavythread \
+check_PROGRAMS = testsig testsegv testbuffer testmemory heavy heavywq heavythread \
 		testprivs teststream testchecksum tabletest testnexthopiter \
 		$(TESTS_BGPD)
 
 noinst_HEADERS = prng.h
 
 testsig_SOURCES = test-sig.c
+testsegv_SOURCES = test-segv.c
 testbuffer_SOURCES = test-buffer.c
 testmemory_SOURCES = test-memory.c
 testprivs_SOURCES = test-privs.c
@@ -48,6 +49,7 @@
 testnexthopiter_SOURCES = test-nexthop-iter.c prng.c
 
 testsig_LDADD = ../lib/libzebra.la @LIBCAP@
+testsegv_LDADD = ../lib/libzebra.la @LIBCAP@
 testbuffer_LDADD = ../lib/libzebra.la @LIBCAP@
 testmemory_LDADD = ../lib/libzebra.la @LIBCAP@
 testprivs_LDADD = ../lib/libzebra.la @LIBCAP@