git/getStringUntil: fix uninitialized stack variable

at least clang-tidy is not convinced that this initialized.
If this is not the case, the impact should be small and hopefully also
more robust if changed.

src/libutil/git.cc

@@ -33,7 +33,7 @@ std::optional<Mode> decodeMode(RawMode m) {
 static std::string getStringUntil(Source & source, char byte)
 {
     std::string s;
-    char n[1];
+    char n[1] = { 0 };
     source(std::string_view { n, 1 });
     while (*n != byte) {
         s += *n;