xz: Fix message_init() description.

Also explicitly initialize progress_automatic to make it clear
that it can be read before message_init() sets it. Static variable
was initialized to false by default already so this is only for
clarity.

(cherry picked from commit c701a5909ad9882469fbab4fab5d2d5556d3ba78)

src/xz/main.c

@@ -170,7 +170,8 @@ main(int argc, char **argv)
 	// Set up the locale and message translations.
 	tuklib_gettext_init(PACKAGE, LOCALEDIR);
 
-	// Initialize handling of error/warning/other messages.
+	// Initialize progress message handling. It's not always needed
+	// but it's simpler to do this unconditionally.
 	message_init();
 
 	// Set hardware-dependent default values. These can be overridden

src/xz/message.c

@@ -42,7 +42,7 @@ static bool current_filename_printed = false;
 
 /// True if we should print progress indicator and update it automatically
 /// if also verbose >= V_VERBOSE.
-static bool progress_automatic;
+static bool progress_automatic = false;
 
 /// True if message_progress_start() has been called but
 /// message_progress_end() hasn't been called yet.

src/xz/message.h

@@ -24,7 +24,10 @@ enum message_verbosity {
 extern const int message_progress_sigs[];
 
 
-/// \brief      Initializes the message functions
+/// \brief      Initializes the progress message functions
+///
+/// message_fatal() and such can be called even before message_init()
+/// has been called.
 ///
 /// If an error occurs, this function doesn't return.
 ///