Make the VSL skeptical of zero-filled VSM.

include/vsl.h

@@ -66,6 +66,7 @@
  * on this file to extract the table rather than handcode it
  */
 enum VSL_tag_e {
+	SLT_Bogus = 0,
 #define SLTM(foo)	SLT_##foo,
 #include "vsl_tags.h"
 #undef SLTM

lib/libvarnishapi/vsl.c

@@ -173,6 +173,11 @@ vsl_nextlog(struct vsl *vsl, uint32_t **pp)
 	for (w = 0; w < TIMEOUT_USEC;) {
 		t = *vsl->log_ptr;
 
+		if (t == 0) {
+			/* Zero-initialized VSL */
+			VRMB();
+			continue;
+		}
 		if (t == VSL_WRAPMARKER) {
 			/* Wrap around not possible at front */
 			assert(vsl->log_ptr != vsl->log_start + 1);