cooker/providers: Only add target to world build if task exists

A "bitbake world -c unpack" currently breaks as not all tasks have an unpack task. This change allows addition of world targets only if the specified task exists which makes certain commands possible when otherwise you just get errors which can't easily be avoided.

index 0e78106..606b08e 100644
@@ -658,7 +658,7 @@ class BBCooker:

         if task is None:
             task = self.configuration.cmd

-        fulltargetlist = self.checkPackages(pkgs_to_build)
+        fulltargetlist = self.checkPackages(pkgs_to_build, task) taskdata = {}
         localdata = {}

@@ -1586,7 +1586,7 @@ class BBCooker:

         return True

-    def checkPackages(self, pkgs_to_build):
+    def checkPackages(self, pkgs_to_build, task=None):

         # Return a copy, don't modify the original
         pkgs_to_build = pkgs_to_build[:]
@@ -1602,7 +1602,7 @@ class BBCooker:
         if 'world' in pkgs_to_build:
             pkgs_to_build.remove('world')
             for mc in self.multiconfigs:
-                bb.providers.buildWorldTargetList(self.recipecaches[mc]) +                bb.providers.buildWorldTargetList(self.recipecaches[mc], task) for t in self.recipecaches[mc].world_target:
                     if mc:
                         t = "multiconfig:" + mc + ":" + t

index 80701b2..db02a0b 100644
@@ -402,7 +402,7 @@ def getRuntimeProviders(dataCache, rdepend):

     return rproviders


-def buildWorldTargetList(dataCache):
+def buildWorldTargetList(dataCache, task=None):
     """
     Build package list for "bitbake world"
     """
@@ -413,6 +413,9 @@ def buildWorldTargetList(dataCache):
     for f in dataCache.possible_world:
         terminal = True
         pn = dataCache.pkg_fn[f]
+        if task and task not in dataCache.task_deps[f]['tasks']:
+            logger.debug(2, "World build skipping %s as task %s doesn't exist", f, task) +            terminal = False

         for p in dataCache.pn_provides[pn]:
             if p.startswith('virtual/'):