Fix bug in InterpretNode.asCallable

It was only working for summarized callables.

Author: owen-mc

go/ql/lib/semmle/go/dataflow/internal/FlowSummaryImpl.qll

@@ -252,7 +252,9 @@ module SourceSinkInterpretationInput implements
 
     /** Gets the callable that this node corresponds to, if any. */
     DataFlowCallable asCallable() {
-      result.asSummarizedCallable().asFunction() = this.asElement().asEntity()
+      this.asElement().asEntity() = result.asSummarizedCallable().asFunction() or
+      this.asElement().asEntity() = result.asCallable().asFunction() or
+      this.asElement().asAstNode() = result.asCallable().asFuncLit()
     }
 
     /** Gets the target of this call, if any. */

go/ql/test/library-tests/semmle/go/dataflow/ExternalTaintFlow/srcs.expected

@@ -22,3 +22,4 @@ invalidModelRow
 | test.go:187:24:187:31 | call to Src1 | qltest |
 | test.go:191:24:191:31 | call to Src1 | qltest |
 | test.go:201:10:201:28 | selection of SourceVariable | qltest |
+| test.go:205:15:205:17 | definition of src | qltest |

go/ql/test/library-tests/semmle/go/dataflow/ExternalTaintFlow/test.go

@@ -203,7 +203,7 @@ func simpleflow() {
 }
 
 func srcParam(src string, b test.B) {
-	b.Sink1(src) // $ MISSING: hasTaintFlow="src"
+	b.Sink1(src) // $ hasTaintFlow="src"
 }
 
 type mapstringstringtype map[string]string