Oops, clear hovered icon in the text window when the mouse leaves

that window; otherwise it remains highlighted, and may even get
tooltipped.

[git-p4: depot-paths = "//depot/solvespace/": change = 2134]

textwin.cpp

@@ -597,6 +597,7 @@ done:
 
 void TextWindow::MouseLeave(void) {
     tooltippedIcon = NULL;
+    hoveredIcon = NULL;
     hoveredRow = 0;
     hoveredCol = 0;
     InvalidateText();