Better bound check.

[nissaba]

Hello, It would be nice that instead of rejecting a pan action that gives a invalid pan that instead of rejecting it that it tries to correct it or at least limits the transforme so that the values do not go beyond the edges. the way it is now it difficult to get the image to the edges for example: right after the initial load try to set the image to the top left corner. you will not be able to get the top part.