[Patch] sanitize formula breaking when pressing C-Enter in a simple formula

[Martin Vermeer]

This sanitizes the behaviour. This was a major irritant for me. Start
typing a formula, like E = mc^2, and press Control-Enter. The "= mc^2"
goes to the next line, which in 99% of cases we don't want.

- Martin

Index: InsetMathHull.cpp
===================================================================
--- InsetMathHull.cpp	(revision 20732)
+++ InsetMathHull.cpp	(working copy)
@@ -717,6 +717,7 @@
 			cell(i).erase(1, cell(i).size());
 		}
 	}
+
 }
 
 
@@ -1056,7 +1057,7 @@
 			bool const align =
 				cur.bv().buffer().params().use_amsmath == BufferParams::package_on;
 			mutate(align ? hullAlign : hullEqnArray);
-			cur.idx() = 0;
+			cur.idx() = nrows() * ncols() - 1;
 			cur.pos() = cur.lastpos();
 		}
 		InsetMathGrid::doDispatch(cur, cmd);