avatar-chooser: Don't call clear_image() from ::init()
avatar-chooser: Don't call clear_image() from ::init()

GtkButton currently has a bug where calling gtk_button_set_image() in
the ::init() vfunc of a subclass will cause the GtkImage to be leaked.
This bug does not happen if the image is set after the GtkButton has
been constructed, so this commit moves the call to
avatar_chooser_clear_image() (which calls gtk_button_set_image()) from
::init() to ::constructed().

See https://bugzilla.gnome.org/show_bug.cgi?id=753048

This fixes:

==388== 768 (304 direct, 464 indirect) bytes in 1 blocks are definitely lost in loss record 33,655 of 34,
==388==    at 0x8792D9C: g_type_create_instance (gtype.c:1849)
==388==    by 0x8779AC5: g_object_new_internal (gobject.c:1774)
==388==    by 0x8779FD4: g_object_newv (gobject.c:1921)
==388==    by 0x8779676: g_object_new (gobject.c:1614)
==388==    by 0x7453142: gtk_image_new_from_icon_name (gtkimage.c:792)
==388==    by 0x4CC2CEE: avatar_chooser_clear_image (tpaw-avatar-chooser.c:394)
==388==    by 0x4CC45AA: tpaw_avatar_chooser_init (tpaw-avatar-chooser.c:1195)
==388==    by 0x8792E7D: g_type_create_instance (gtype.c:1870)
==388==    by 0x8779AC5: g_object_new_internal (gobject.c:1774)
==388==    by 0x877A71A: g_object_new_valist (gobject.c:2033)
==388==    by 0x87796C5: g_object_new (gobject.c:1617)
==388==    by 0x4CC4673: tpaw_avatar_chooser_new (tpaw-avatar-chooser.c:1213)
==388==    by 0x4CD41D2: tpaw_user_info_constructed (tpaw-user-info.c:543)
==388==    by 0x8779C10: g_object_new_internal (gobject.c:1814)
==388==    by 0x877A71A: g_object_new_valist (gobject.c:2033)
==388==    by 0x87796C5: g_object_new (gobject.c:1617)
==388==    by 0x4CD4826: tpaw_user_info_new (tpaw-user-info.c:663)
==388==    by 0x4C97906: edit_personal_details (goatelepathyprovider.c:667)
==388==    by 0x4C980A7: edit_personal_details_clicked_cb (goatelepathyprovider.c:859)
==388==    by 0x877427D: g_cclosure_marshal_VOID__VOIDv (gmarshal.c:905)
==388==    by 0x87714D1: _g_closure_invoke_va (gclosure.c:864)
==388==    by 0x878C771: g_signal_emit_valist (gsignal.c:3246)
==388==    by 0x878D8E9: g_signal_emit (gsignal.c:3393)
==388==    by 0x7326A22: gtk_button_clicked (gtkbutton.c:1488)
==388==    by 0x7327943: gtk_button_do_release (gtkbutton.c:1899)
==388==    by 0x7327D22: gtk_real_button_released (gtkbutton.c:2017)
==388==    by 0x877427D: g_cclosure_marshal_VOID__VOIDv (gmarshal.c:905)
==388==    by 0x877190F: g_type_class_meta_marshalv (gclosure.c:1021)
==388==    by 0x87714D1: _g_closure_invoke_va (gclosure.c:864)
==388==    by 0x878C771: g_signal_emit_valist (gsignal.c:3246)
==388==    by 0x878D8E9: g_signal_emit (gsignal.c:3393)
==388==    by 0x73244D2: multipress_released_cb (gtkbutton.c:613)
==388==    by 0x36E5A05DAF: ffi_call_unix64 (unix64.S:76)
==388==    by 0x36E5A05817: ffi_call (ffi64.c:525)
==388==    by 0x8772F7C: g_cclosure_marshal_generic_va (gclosure.c:1594)
==388==    by 0x87714D1: _g_closure_invoke_va (gclosure.c:864)
==388==    by 0x878C771: g_signal_emit_valist (gsignal.c:3246)
==388==    by 0x878D8E9: g_signal_emit (gsignal.c:3393)
==388==    by 0x7421792: gtk_gesture_multi_press_end (gtkgesturemultipress.c:273)
==388==    by 0x8775B90: g_cclosure_marshal_VOID__BOXEDv (gmarshal.c:1950)

https://bugzilla.gnome.org/show_bug.cgi?id=752938

Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets