#136 Assertion failures and warnings on file opening

[MM]

Following assertion failures and warnings appear on opending the test file attached to the ticket 121 ( https://sourceforge.net/p/projectlibre/tickets/121/attachment/Test_project.pod ):

(java:3186): GLib-GObject-WARNING **: invalid cast from 'JawImpl_4098' to 'AtkText'

** (java:3186): CRITICAL **: atk_text_get_character_count: assertion 'ATK_IS_TEXT (text)' failed

(java:3186): GLib-GObject-WARNING **: ../../../../gobject/gsignal.c:3492: signal name 'text_changed::delete' is invalid for instance '0x7f8b48074530' of type 'JawImpl_4098'

(java:3186): GLib-GObject-WARNING **: invalid cast from 'JawImpl_4098' to 'AtkText'

** (java:3186): CRITICAL **: atk_text_get_character_count: assertion 'ATK_IS_TEXT (text)' failed

Test steps:

1. Start ProjectLibre by running sh [...]/projectlibre.sh in the terminal
2. In the selection dialog (whether to create a new project or open an existing one), select "Open" and open the above test file. Observe the terminal output.

Tested with the current projectlibre-1.7.0.zip (running as non-admin user, without installation) on Ubuntu 17.04 Mate, 64-bit.

openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.17.04.3-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)