fixed typo in gtktextview.c
The following Merge Request (MR) has been forwarded from GitHub in order to prevent the GNOME Project from losing contributions coming from un-official channels. And for contributors to not see their valuable contributions not being accounted for.
Relevant information:
Github handle: AndrewAlfazy
MR URL: https://github.com/GNOME/gtk/pull/21
Patch URL: https://github.com/GNOME/gtk/pull/21.patch
Body of the MR: