Fixed typos in MeshDataTool documentation

- Fixed missing "be" typo in MeshDataTool's get_face_edge function
- Corrected documentation to say negative values aren't valid

(cherry picked from commit bc9df365b045419e26763859019cd1111103ac4e)

doc/classes/MeshDataTool.xml

@@ -93,7 +93,7 @@
 			<argument index="1" name="edge" type="int" />
 			<description>
 				Returns specified edge associated with given face.
-				Edge argument must 2 or less because a face only has three edges.
+				Edge argument must be either 0, 1, or 2 because a face only has three edges.
 			</description>
 		</method>
 		<method name="get_face_meta" qualifiers="const">
@@ -116,7 +116,7 @@
 			<argument index="1" name="vertex" type="int" />
 			<description>
 				Returns the specified vertex of the given face.
-				Vertex argument must be 2 or less because faces contain three vertices.
+				Vertex argument must be either 0, 1, or 2 because faces contain three vertices.
 			</description>
 		</method>
 		<method name="get_format" qualifiers="const">