fix: check if timer variable is nullptr

Author: Zishan Mirza

libc/src/time/linux/localtime_r.cpp

@@ -13,6 +13,10 @@ namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(struct tm *, localtime_r,
                    (const time_t *timer, struct tm *buf)) {
+  if (timer == nullptr) {
+    return nullptr;
+  }
+
   return time_utils::localtime_internal(timer, buf);
 }
 

libc/src/time/linux/localtime_s.cpp

@@ -13,6 +13,10 @@ namespace LIBC_NAMESPACE_DECL {
 
 // windows only, implemented in gnu/linux for compatibility reasons
 LLVM_LIBC_FUNCTION(int, localtime_s, (const time_t *timer, struct tm *input)) {
+  if (timer == nullptr) {
+    return nullptr;
+  }
+
   return time_utils::localtime_s_internal(timer, input);
 }