Handle nil when looking up a file by position into a package (#747)

analyzer.go

@@ -219,7 +219,12 @@ func (gosec *Analyzer) load(pkgPath string, conf *packages.Config) ([]*packages.
 func (gosec *Analyzer) Check(pkg *packages.Package) {
 	gosec.logger.Println("Checking package:", pkg.Name)
 	for _, file := range pkg.Syntax {
-		checkedFile := pkg.Fset.File(file.Pos()).Name()
+		fp := pkg.Fset.File(file.Pos())
+		if fp == nil {
+			// skip files which cannot be located
+			continue
+		}
+		checkedFile := fp.Name()
 		// Skip the no-Go file from analysis (e.g. a Cgo files is expanded in 3 different files
 		// stored in the cache which do not need to by analyzed)
 		if filepath.Ext(checkedFile) != ".go" {