wpesrc: plug some small leaks.

commit c44b7cfc

wpesrc: add some debug logging around WPEView creation/destruction

commit fc03d1ad

wpesrc: fix a memory leak of the bytes

free the previous GBytes if load-bytes is called multiple times
before view creation.

commit 68314f41

wpesrc: only create webview if not already created

e.g. _decide_allocation() can be called multiple times throughout the
element's lifetime and we only want to create the view once rather than
overwriting.

Fixes a leak of the WPEView under certain circumstances.

commit 72ee84a2

wpe: free a previous pending image/shm buffer

Don't blindly overwrite a possibly previously set buffer.