don't square error term twice

The cubic code erroneously passed the error square term to a function
which in turn squares the error term.

R=reed@google.com
BUG=skia:3877

Review URL: https://codereview.chromium.org/1163843003
diff --git a/src/core/SkStroke.cpp b/src/core/SkStroke.cpp
index a05bfd4..2589cf6 100644
--- a/src/core/SkStroke.cpp
+++ b/src/core/SkStroke.cpp
@@ -1039,7 +1039,7 @@
             }
             if ((kDegenerate_ResultType == resultType
                     || points_within_dist(quadPts->fQuad[0], quadPts->fQuad[2],
-                    fInvResScaleSquared)) && cubicMidOnLine(cubic, quadPts)) {
+                    fInvResScale)) && cubicMidOnLine(cubic, quadPts)) {
                 addDegenerateLine(quadPts);
                 return true;
             }