fix calculation of position area if tabs are involved

Signed-off-by: Florian Thienel <florian@thienel.org>
diff --git a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/boxes/TextContent.java b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/boxes/TextContent.java
index 277d2a7..1075eb5 100644
--- a/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/boxes/TextContent.java
+++ b/org.eclipse.vex.core/src/org/eclipse/vex/core/internal/boxes/TextContent.java
@@ -451,7 +451,7 @@
 		final char c = content.charAt(offset);
 		final String head = renderText(content.subSequence(startPosition.getOffset(), offset).toString());
 		final int left = graphics.stringWidth(head);
-		final int charWidth = graphics.stringWidth(Character.toString(c));
+		final int charWidth = graphics.stringWidth(renderText(Character.toString(c)));
 		return new Rectangle(left, 0, charWidth, height);
 	}