Initialize some uninitialized pointers

The compiler was complaining that some of these pointers could be
uninitialized under some optimization levels (especially when no-opping
logging for fuzzing). This change addresses that.

Bug: None
Test: make tests
Change-Id: I7ead341ad7c1ef2770ba131a83ba20710ee3302d
diff --git a/syscall_filter.c b/syscall_filter.c
index adc4b3c..c338e90 100644
--- a/syscall_filter.c
+++ b/syscall_filter.c
@@ -173,7 +173,7 @@
 		 struct bpf_labels *labels, int nr, int grp_idx)
 {
 	/* Splits the atom. */
-	char *atom_ptr;
+	char *atom_ptr = NULL;
 	char *argidx_str = strtok_r(atom, " ", &atom_ptr);
 	if (argidx_str == NULL) {
 		warn("empty atom");