Bug 338675

I have a UC-LOGIC TWA60 tablet which Krita recognizes on startup.  However, it refuses to detect any sort of pressure regardless of what value the tablet is actually sending: http://i.imgur.com/Jh6jsK4.gif.

Reproducible: Always

Steps to Reproduce:
1. Start Krita with UC-LOGIC TWA60 tablet plugged in
2. Enable pressure sensitivity
3. Attempt to draw a line using the tablet

Actual Results:  
The line stays the same thickness/weight regardless of the pressure applied.

Expected Results:  
The line should vary in thickness/weight depending on pressure applied.

So after a long debugging session, I managed to track down where this is happening.  In ui/input/wintab/kis_tablet_support_x11.cpp on line 608 there is a test to make sure that the tablet is returning "sane data".  If this checks out false, it returns early and ignores any pressure or other input from the tablet.  The check calls to ui/input/wintab/kis_tablet_support.h on line 149 which returns the result of "firstAxis <= m_lastSaneAxis".  When debugging, "firstAxis" appears to be an normal value but "m_lastSaneAxis" appears to be a random negative number.  Running a search in the code for "m_lastSaneAxis" turns up that it's only two uses are a declaration on line 162 and it's use on line 157.  That means it's uninitialized and the comparison will fail if the memory at that point happens to be a negative integer.  Initializing it to a positive integer seems to fix this problem.