JS: Fix bad join

Author: asgerf

javascript/ql/lib/semmle/javascript/dependencies/Dependencies.qll

@@ -151,6 +151,11 @@ class ExternalNpmDependency extends NpmDependency {
   }
 }
 
+pragma[nomagic]
+private string getImportedPackage(Import i) {
+  result = i.getImportedPathString().(StringAsPath).getPackagePrefix()
+}
+
 /**
  * Holds if import `i` may refer to the declared dependency `dep` of package `pkg`,
  * where the result value is the nesting depth of the file containing `i` within `pkg`.
@@ -159,7 +164,7 @@ private int importsDependency(Import i, NpmPackage pkg, NpmDependency dep) {
   exists(string name |
     dep = pkg.getPackageJson().getADependenciesObject(_).getPropValue(name) and
     not exists(i.getImportedModule()) and
-    name = i.getImportedPathString().(StringAsPath).getPackagePrefix() and
+    name = getImportedPackage(i) and
     i.getEnclosingModule() = pkg.getAModule() and
     result = distance(pkg, i.getFile())
   )