ossdataflowengine: fix edge case when tracking from receivers

dataflowengineoss/src/main/scala/io/joern/dataflowengineoss/queryengine/SourcesToStartingPoints.scala

@@ -81,6 +81,8 @@ class SourceToStartingPoints(src: StoredNode) extends RecursiveTask[List[CfgNode
         withFieldAndIndexAccesses(
           List(x).collectAll[CfgNode].toList ++ x.refsTo.collectAll[Local].flatMap(sourceToStartingPoints)
         ) ++ x.refsTo.capturedByMethodRef.referencedMethod.flatMap(m => usagesForName(x.name, m))
+      case x: Call =>
+        (x._receiverIn.l ++ List(x)).collect { case y: CfgNode => y }
       case x => List(x).collect { case y: CfgNode => y }
     }
   }

joern-cli/frontends/pysrc2cpg/src/test/scala/io/joern/pysrc2cpg/dataflow/DataFlowTests.scala

@@ -446,4 +446,18 @@ class RegexDefinedFlowsDataFlowTests
     }
   }
 
+  "flows from receivers" should {
+    val cpg = code("""
+        |class Foo:
+        |   def func():
+        |      return "x"
+        |print(Foo.func())
+        |""".stripMargin)
+    "be found" in {
+      val src = cpg.call.code("Foo.func").l
+      val snk = cpg.call("print").l
+      snk.argument.reachableByFlows(src).size shouldBe 1
+    }
+  }
+
 }