Avoid heap-buffer-overflow if xdata of patch object is a row vector (…

…bug #66466).

* libinterp/corefcn/graphics.cc (patch::properties::update_fvc): The "xdata"
property of a patch graphics object is allowed to be a row vector (in which
case it is treated like a column vector). In this case, check whether colors
are set per vertex after the input has been transformed to column vectors. This
avoids a potential heap-buffer-overflow when creating the "facevertexcdata" of
the patch graphics object.

libinterp/corefcn/graphics.cc

@@ -9691,10 +9691,6 @@ patch::properties::update_fvc ()
       return;
     }
 
-  bool pervertex = false;
-  if (ncv == nv)
-    pervertex = true;
-
   bool isRGB = false;
   if (cd.ndims () == 3)
     isRGB = true;
@@ -9711,6 +9707,10 @@ patch::properties::update_fvc ()
       zd = zd.as_column ();
     }
 
+  bool pervertex = false;
+  if (ncv == nv)
+    pervertex = true;
+
   dv(0) = nv * nf;
   if (zd.isempty ())
     dv(1) = 2;