KDEGitCommitHooks: don't overwrite git pre-commit hook script
If the .git/hooks/pre-commit already exists, only add the clang-format line if it doesn't already exist.
If clang-format isn't found, there is nothing to write to the file.
If the .git/hooks/pre-commit already exists, only add the clang-format line if it doesn't already exist.
If clang-format isn't found, there is nothing to write to the file.