Fixes the s shift s bug

The s shift s bug is reported here
PartialVolume/shredos.x86_64#301

To summarize, if no drives are selected and then the user presses
s (lower case) a warning appears indicating that the user
should press S (upper case) to start the wipe. This
warning appears for about 3 seconds but during this time if the
user presses S (upper case) nwipe would immediately complete,
having wiped no drives and requesting the user to press the
spacebar to exit. The is incorrect behaviour.
The bug doesn't appear if the user pressed S after the 3
seconds elapsed and the warning message disappeared.

This patch fixes this so that it does not exit but displays the
warning for 3 seconds and then waits for input.

src/gui.c

@@ -669,6 +669,10 @@ void nwipe_gui_select( int count, nwipe_context_t** c )
     /* Control A toggle status -1=indefined, 0=all drives delected, 1=all drives selected */
     int select_all_toggle_status = -1;
 
+    /* This is a flag used to exit this function once drives are selected and S is pressed 0=do not start wipe, 1=start
+     * wipe */
+    int startwipe = 0;
+
     /* Get the terminal size */
     getmaxyx( stdscr, stdscr_lines, stdscr_cols );
 
@@ -1304,6 +1308,10 @@ void nwipe_gui_select( int count, nwipe_context_t** c )
                         /* Remove the S from keystroke, which allows us to stay within the selection menu loop */
                         keystroke = 0;
                     }
+                    else
+                    {
+                        startwipe = 1;
+                    }
 
                     break;
 
@@ -1402,9 +1410,9 @@ void nwipe_gui_select( int count, nwipe_context_t** c )
         while( validkeyhit == 0 && terminate_signal != 1 && stdscr_cols_previous == stdscr_cols
                && stdscr_lines_previous == stdscr_lines );
 
-    } while( keystroke != 'S' && terminate_signal != 1 );
+    } while( startwipe == 0 && terminate_signal != 1 );
 
-    if( keystroke == 'S' )
+    if( startwipe == 1 )
     {
         /* If user has pressed S to start wipe change status line */
         werase( footer_window );