Fixed constantly mipmap generation

Fixed bug when setting MinFilter with mipmapping after generating mipmaps causes jME to update image data every frame.

jme3-core/src/main/java/com/jme3/texture/Texture.java

@@ -339,7 +339,7 @@ public abstract class Texture implements CloneableSmartAsset, Savable, Cloneable
                     "minificationFilter can not be null.");
         }
         this.minificationFilter = minificationFilter;
-        if (minificationFilter.usesMipMapLevels() && image != null && !image.isGeneratedMipmapsRequired()) {
+        if (minificationFilter.usesMipMapLevels() && image != null && !image.isGeneratedMipmapsRequired() && !image.hasMipmaps()) {
             image.setNeedGeneratedMipmaps();
         }
     }
@@ -631,4 +631,4 @@ public abstract class Texture implements CloneableSmartAsset, Savable, Cloneable
     }
     
     
-}
+}