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.

(cherry picked from commit 7e540059a3)

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;