bitbake: bitbake: hob/builder: Hob crashes because of bad init

Image selection is not properly initialized to none,
and it used before having a chance to have a value.
Due to dynamic nature of Python, variable is used before
it exists, in this case. This causes a crash.
Bug introduced during the fix of [YOCTO #3228]

Fixes [YOCTO #3334]

(Bitbake rev: 1c540541c5397c38dca880a79df9ebfcda576d4c)

Signed-off-by: Cristian Iorga <cristian.iorga@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/ui/crumbs/builder.py

@@ -89,6 +89,7 @@ class Configuration:
 
     def __init__(self):
         self.curr_mach = ""
+        self.selected_image = None
         # settings
         self.curr_distro = ""
         self.dldir = self.sstatedir = self.sstatemirror = ""