text-on-path: truncated text not reported in all cases

[su_v]

Inkscape 0.48 introduced status bar notifications for truncated text (flowed text, text-on-path):
<quote>
When a flowed text is truncated (i.e. the frame is too small for the entire text), the frame is shown red, and the statusbar hint includes [truncated]. You need to resize the frame to see the truncated end of the text. Analogously, if the path of a text-on-path object is too short to display the entire text, the statusbar will report it as [truncated]
</quote>
http://wiki.inkscape.org/wiki/index.php/Release_notes/0.48#Other_features

For text put on path, these notifications are not generated for center-aligned or right-aligned text with a startOffset close to or at the start of the path; other cases (right-aligned at start; center-aligned near/at end; left-aligned near/at end) produce '[truncated]' notifications as expected.

Steps to reproduce:
1) launch current stable inkscape
   (default new doc, default prefs)
2) create a text object
3) draw a straight line
4) select all, put text on path
5) open Text and Font
6) change alignment to 'Center', click apply

-> the left half of the text is truncated, no hint in the status bar.

7) change startOffset to 100%

-> the right half of the text is truncated, hint displayed as expected in the status bar.

8) repeat tests with left-aligned at 90%, right-aligned at 10%

-> hints are only displayed for text that is partially truncated at the end of the path.

9) repeat test with left-aligned at 100%, right-aligned at 0%

-> hint is displayed as expected (text is fully truncated in both cases).

Reproduced with Inkscape 0.48.x, 0.91, 0.92.1 on OS X 10.7.5,
Reproduced with 0.92.1, lp:inkscape r15556 + patch from bug #1619557 on Windows 10.