merge_files: don't add trailing newlines

When invoked with three files that each lack a trailing newline,
the merge result should also lack a trailing newline.

tests/merge/files.c

@@ -249,3 +249,42 @@ void test_merge_files__automerge_whitespace_change(void)
 
 	git_merge_file_result_free(&result);
 }
+
+void test_merge_files__doesnt_add_newline(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
+	const char *expected = "Zero\n1\n2\n3\n4\n5 XXX\n6 YYY\n7\n8\n9\nTen";
+
+	ancestor.ptr = "0\n1\n2\n3\n4\n5 XXX\n6YYY\n7\n8\n9\n10";
+	ancestor.size = strlen(ancestor.ptr);
+	ancestor.path = "testfile.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr = "Zero\n1\n2\n3\n4\n5 XXX\n6 YYY\n7\n8\n9\n10";
+	ours.size = strlen(ours.ptr);
+	ours.path = "testfile.txt";
+	ours.mode = 0100755;
+
+	theirs.ptr = "0\n1\n2\n3\n4\n5 XXX\n6  YYY\n7\n8\n9\nTen";
+	theirs.size = strlen(theirs.ptr);
+	theirs.path = "testfile.txt";
+	theirs.mode = 0100755;
+
+	opts.flags |= GIT_MERGE_FILE_IGNORE_WHITESPACE_CHANGE;
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, &opts));
+
+	cl_assert_equal_i(1, result.automergeable);
+
+	cl_assert_equal_s("testfile.txt", result.path);
+	cl_assert_equal_i(0100755, result.mode);
+
+	cl_assert_equal_i(strlen(expected), result.len);
+	cl_assert_equal_strn(expected, result.ptr, result.len);
+
+	git_merge_file_result_free(&result);
+}
+