bug#9983: valgrind warning in draw_glyphs

[Dan Nicolaescu <dann@gnu.org>]

trunk with lucid toolkit
valgrind ./temacs -Q
gives this warning (not sure exactly when, just playing with the menus
and tooltips, the only "editing" action was to run a grep)





==2341== Conditional jump or move depends on uninitialised value(s)
==2341==    at 0x44CDDA: draw_glyphs (xdisp.c:22981)
==2341==    by 0x44D9FC: expose_area (xdisp.c:27401)
==2341==    by 0x44DDA8: expose_line (xdisp.c:27426)
==2341==    by 0x45B6AA: expose_window (xdisp.c:27653)
==2341==    by 0x45C0DA: expose_window_tree (xdisp.c:27725)
==2341==    by 0x45C0B0: expose_window_tree (xdisp.c:27723)
==2341==    by 0x45C16E: expose_frame (xdisp.c:27780)
==2341==    by 0x4C188D: handle_one_xevent (xterm.c:6219)
==2341==    by 0x4C2F56: XTread_socket (xterm.c:7148)
==2341==    by 0x4F2F26: read_avail_input (keyboard.c:6821)
==2341==    by 0x4F3049: handle_async_input (keyboard.c:7149)
==2341==    by 0x4F26A4: process_pending_signals (keyboard.c:7165)
==2341==  Uninitialised value was created by a stack allocation
==2341==    at 0x44AAD3: draw_glyphs (xdisp.c:22835)
==2341== 


The warning is for this:
        if (check_mouse_face
              && mouse_beg_col < start && mouse_end_col > i)

it looks like mouse_beg_col and mouse_end_col could be left uninitialized a few lines above.