Fix crash due to std::string_view change
std::string_view can't accept a null pointer.
diff --git a/src/regen.cc b/src/regen.cc
index 0f2bb1c..458c4cd 100644
--- a/src/regen.cc
+++ b/src/regen.cc
@@ -202,7 +202,8 @@
int num_envs = LOAD_INT(fp);
for (int i = 0; i < num_envs; i++) {
LOAD_STRING(fp, &s);
- std::string_view val(getenv(s.c_str()));
+ const char* val_c_str = getenv(s.c_str());
+ std::string_view val(val_c_str ? val_c_str : "");
LOAD_STRING(fp, &s2);
if (val != s2) {
if (g_flags.dump_kati_stamp) {
