Merge pull request #11337 from NixOS/backport-11332-to-2.19-maintenance

[Backport 2.19-maintenance] [Backport 2.22-maintenance] fix: check to see if there are any lines before

src/nix-build/nix-build.cc

@@ -133,7 +133,7 @@ static void main_nix_build(int argc, char * * argv)
         script = argv[1];
         try {
             auto lines = tokenizeString<Strings>(readFile(script), "\n");
-            if (std::regex_search(lines.front(), std::regex("^#!"))) {
+            if (!lines.empty() && std::regex_search(lines.front(), std::regex("^#!"))) {
                 lines.pop_front();
                 inShebang = true;
                 for (int i = 2; i < argc; ++i)