Python: Fix bad join in import_star_read

Makes this

```
(21s) Tuple counts for DataFlowPublic::import_star_read#ff/2@fcd5e6nr after 8.5s:
9743      ~6%     {3} r1 = SCAN num#DataFlowPublic::TModuleVariableNode#fff OUTPUT In.1, In.0, In.2 'result'
9743      ~1%     {3} r2 = JOIN r1 WITH Variables::Variable::getId_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2 'result'
390808917 ~3%     {3} r3 = JOIN r2 WITH Flow::NameNode::getId_dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2 'result'
307       ~0%     {2} r4 = JOIN r3 WITH ImportStar::ImportStar::importStarResolvesTo#ff ON FIRST 2 OUTPUT Lhs.0, Lhs.2 'result'
307       ~0%     {2} r5 = JOIN r4 WITH num#DataFlowPublic::TCfgNode#ff ON FIRST 1 OUTPUT Rhs.1 'n', Lhs.1 'result'
                  return r5
```

become this

```
(17s) Tuple counts for DataFlowPublic::resolved_import_star_module#fff/3@f5e84aic after 0ms:
307 ~0%     {3} r1 = JOIN ImportStar::ImportStar::importStarResolvesTo#ff WITH num#DataFlowPublic::TCfgNode#ff ON FIRST 1 OUTPUT Lhs.0, Lhs.1 'm', Rhs.1 'n'
307 ~0%     {3} r2 = JOIN r1 WITH Flow::NameNode::getId_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'm', Rhs.1 'name', Lhs.2 'n'
            return r2
(17s) Registering DataFlowPublic::resolved_import_star_module#fff/3@f5e84aic +  with content f29281ig38r98icro4ege09mrva
(17s)  >>> Created relation DataFlowPublic::resolved_import_star_module#fff/3@f5e84aic with 307 rows.
(17s) Starting to evaluate predicate DataFlowPublic::import_star_read#ff/2@57b0c06e
(17s) Tuple counts for DataFlowPublic::import_star_read#ff/2@57b0c06e after 2ms:
9743 ~0%     {3} r1 = SCAN num#DataFlowPublic::TModuleVariableNode#fff OUTPUT In.1, In.0, In.2 'result'
9743 ~0%     {3} r2 = JOIN r1 WITH Variables::Variable::getId_dispred#ff ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.2 'result'
307  ~0%     {2} r3 = JOIN r2 WITH DataFlowPublic::resolved_import_star_module#fff ON FIRST 2 OUTPUT Rhs.2 'n', Lhs.2 'result'
             return r3
```

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPublic.qll

@@ -401,8 +401,15 @@ class ModuleVariableNode extends Node, TModuleVariableNode {
 private predicate isAccessedThroughImportStar(Module m) { m = ImportStar::getStarImported(_) }
 
 private ModuleVariableNode import_star_read(Node n) {
-  ImportStar::importStarResolvesTo(n.asCfgNode(), result.getModule()) and
-  n.asCfgNode().(NameNode).getId() = result.getVariable().getId()
+  resolved_import_star_module(result.getModule(), result.getVariable().getId(), n)
+}
+
+pragma[nomagic]
+private predicate resolved_import_star_module(Module m, string name, Node n) {
+  exists(NameNode nn | nn = n.asCfgNode() |
+    ImportStar::importStarResolvesTo(pragma[only_bind_into](nn), m) and
+    nn.getId() = name
+  )
 }
 
 /**