remove the code to handle a nil file.Imports

I could not reproduce the supposed panic, even after I was able to reach
a nil x.Imports in that line in question with the modified test.

strings.go

@@ -42,15 +42,8 @@ func obfuscateLiterals(files []*ast.File) []*ast.File {
 			}
 			x.Decls = append(x.Decls, funcStmt)
 			x.Decls = append(x.Decls, keyStmt(key))
-
-			if x.Imports == nil {
-				newDecls := []ast.Decl{cryptoAesImportSpec}
-				newDecls = append(newDecls, x.Decls...)
-				x.Decls = newDecls
-			} else {
-				astutil.AddImport(fset, x, "crypto/aes")
-				astutil.AddImport(fset, x, "crypto/cipher")
-			}
+			astutil.AddImport(fset, x, "crypto/aes")
+			astutil.AddImport(fset, x, "crypto/cipher")
 
 			addedToPkg = true
 		case *ast.BasicLit:

testdata/scripts/strings.txt

@@ -1,6 +1,6 @@
 
-garble -literals build main.go
-exec ./main
+garble -literals build
+exec ./main$exe
 cmp stdout main.stdout
 ! binsubstr main$exe 'Lorem' 'ipsum' 'dolor' 'first assign' 'second assign' 'First Line' 'Second Line' 'map value' 'to obfuscate' 'also obfuscate'
 
@@ -11,9 +11,11 @@ binsubstr main$exe 'Skip this block,' 'also skip this'
 # Also check that the binary is reproducible.
 cp main$exe main_old$exe
 rm main$exe
-garble -literals build main.go
+garble -literals build
 bincmp main$exe main_old$exe
 
+-- go.mod --
+module test/main
 -- main.go --
 package main
 
@@ -48,8 +50,6 @@ var array [arrayLen]byte
 
 type typeAlias [arrayLen]byte
 
-var variable = "ipsum"
-
 func main() {
 	empty := ""
 
@@ -83,6 +83,14 @@ func main() {
 	fmt.Println(i, foo, bar)
 }
 
+-- decl_without_imports.go --
+package main
+
+// The lack of imports is an edge case, since we have to add imports like
+// crypto/aes.
+
+var variable = "ipsum"
+
 -- main.stdout --
 Lorem
 First Line
@@ -96,4 +104,4 @@ also obfuscate
 map value
 another literal
 Skip this block, also skip this
-1 0 1
+1 0 1