fixed Issue in MeshLoader introduce in a previous commit

jme3-plugins/src/ogre/java/com/jme3/scene/plugins/ogre/MeshLoader.java

@@ -430,7 +430,7 @@ public class MeshLoader extends DefaultHandler implements AssetLoader {
         int texCoords = parseInt(attribs.getValue("texture_coords"), 0);
         for (int i = 0; i < texCoords; i++) {
             String dimsStr = attribs.getValue("texture_coord_dimensions_" + i);
-            if (dimsStr.startsWith("float")) {
+            if (dimsStr != null && dimsStr.startsWith("float")) {
                 dimsStr = dimsStr.substring("float".length());
             }
             int dims = parseInt(dimsStr, 2);