git: add guards against malformed Git config data

Add some checks/guards against malformed data output from Git
configuration when enumerating all entries.

If we hit the unexpected end of the data stream we trace and stop
parsing.

Author: mjcheetham

src/shared/Microsoft.Git.CredentialManager/GitConfiguration.cs

@@ -145,29 +145,47 @@ public void Enumerate(GitConfigurationLevel level, GitConfigurationEnumerationCa
                     value.Clear();
 
                     // Read config scope (null terminated)
-                    while (data[i] != '\0')
+                    while (i < data.Length && data[i] != '\0')
                     {
                         scope.Append(data[i++]);
                     }
 
+                    if (i >= data.Length)
+                    {
+                        _trace.WriteLine("Invalid Git configuration output. Expected null terminator (\\0) after scope.");
+                        break;
+                    }
+
                     // Skip the null terminator
                     i++;
 
                     // Read key name (LF terminated)
-                    while (data[i] != '\n')
+                    while (i < data.Length && data[i] != '\n')
                     {
                         name.Append(data[i++]);
                     }
 
+                    if (i >= data.Length)
+                    {
+                        _trace.WriteLine("Invalid Git configuration output. Expected newline terminator (\\n) after key.");
+                        break;
+                    }
+
                     // Skip the LF terminator
                     i++;
 
                     // Read value (null terminated)
-                    while (data[i] != '\0')
+                    while (i < data.Length && data[i] != '\0')
                     {
                         value.Append(data[i++]);
                     }
 
+                    if (i >= data.Length)
+                    {
+                        _trace.WriteLine("Invalid Git configuration output. Expected null terminator (\\0) after value.");
+                        break;
+                    }
+
                     // Skip the null terminator
                     i++;