Fixed dataBounds error when all values were inf.

If all values are inf. d = d[mask] will create an empty array. You cannot call min or max on an empty array.

pyqtgraph/graphicsItems/PlotCurveItem.py

@@ -132,7 +132,11 @@ class PlotCurveItem(GraphicsObject):
             if any(np.isinf(b)):
                 mask = np.isfinite(d)
                 d = d[mask]
-                b = (d.min(), d.max())
+                try:
+                    b = (d.min(), d.max())
+                except ValueError:
+                    # d has no size, because all of d is inf.
+                    b = (-1, 1)  # Some default bounds
                 
         elif frac <= 0.0:
             raise Exception("Value for parameter 'frac' must be > 0. (got %s)" % str(frac))