Make inject return the injected program's exit code (#8)

This adds that if a process has ran successfully with inject, the exit code from the child process is returned, instead of always success.

Reviewed-on: https://gitea.tendokyu.moe/TeamTofuShop/capnhook/pulls/8
Co-authored-by: kyoubate-haruka <46010460+kyoubate-haruka@users.noreply.github.com>
Co-committed-by: kyoubate-haruka <46010460+kyoubate-haruka@users.noreply.github.com>

inject/main.c

@@ -21,6 +21,7 @@ int main(int argc, char **argv)
     STARTUPINFO si;
     HRESULT hr;
     BOOL ok;
+    DWORD exitCode;
 
     hr = options_init(&opt, argc, argv);
 
@@ -102,11 +103,16 @@ int main(int argc, char **argv)
     }
 
 end:
+
+    exitCode = ERROR_SUCCESS;
+
     if (pi.hProcess != NULL) {
         if (FAILED(hr)) {
             TerminateProcess(pi.hProcess, EXIT_FAILURE);
         }
 
+        GetExitCodeProcess(pi.hProcess, &exitCode);
+
         CloseHandle(pi.hProcess);
     }
 
@@ -116,7 +122,7 @@ end:
 
     free(cmdline);
 
-    return FAILED(hr) ? EXIT_FAILURE : EXIT_SUCCESS;
+    return FAILED(hr) ? EXIT_FAILURE : exitCode;
 }
 
 static HRESULT inject_dll(HANDLE process, const char *dll_name)