Remove goto after return (this makes the JVM mad)

`function2.decaf` now compiles.

src/main/scala/decaf/backend/JasminBackend.scala

@@ -593,7 +593,14 @@ object JasminBackend extends Backend{
         ("\t" * tabLevel) + s"If$label:\n"                      +
         ("\t" * tabLevel) + s".line ${testBody.pos.line}\n"     +
         emit(className,testBody,localVars,tabLevel + 1, breakable)        +
-        ("\t" * (tabLevel + 1)) + s"goto\tIfDone$label\n"     +
+        (testBody match{
+          case StmtBlock(_,stmts,_) =>
+            if (!stmts.last.isInstanceOf[ReturnStmt])
+              ("\t" * (tabLevel + 1)) + s"goto\tIfDone$label\n"
+            else ""
+          case ReturnStmt(_,_) => ""
+          case _ => ("\t" * (tabLevel + 1)) + s"goto\tIfDone$label\n"
+        })    +
         ("\t" * tabLevel) + s"IfElse$label:\n"                  +
         ("\t" * tabLevel) + s".line ${elseBody.pos.line}\n"     +
         emit(className,elseBody,localVars,tabLevel + 1, breakable)        +

src/test/resources/lab4-samples/passed/function2.j

@@ -0,0 +1,131 @@
+.source function2.decaf
+.class public function2
+.super java/lang/Object
+;
+; standard initializer (calls java.lang.Object's initializer)
+;
+.method public <init>()V
+aload_0
+invokenonvirtual java/lang/Object/<init>()V
+return
+.end method
+.method public static readInt()I
+	.limit stack 5
+	.limit locals 1
+	.line 4
+ReadIntBegin:
+	new	java/io/BufferedReader
+	dup
+	new	java/io/InputStreamReader
+	dup
+	getstatic	java/lang/System/in Ljava/io/InputStream;
+	invokespecial	java/io/InputStreamReader/<init>(Ljava/io/InputStream;)V
+	invokespecial	java/io/BufferedReader/<init>(Ljava/io/Reader;)V
+	invokevirtual	java/io/BufferedReader/readLine()Ljava/lang/String;
+	invokestatic	java/lang/Integer/parseInt(Ljava/lang/String;)I
+ReadIntReturn:
+	ireturn
+ReadIntCatch:
+	astore_0
+	iconst_0
+	ireturn
+.catch java/lang/Exception from ReadIntBegin to ReadIntReturn using ReadIntCatch
+.end method
+
+.method public static readLine()Ljava/lang/String;
+	.limit stack 5
+.limit locals 1
+ReadLineBegin:
+	new java/io/BufferedReader
+	dup
+	new	java/io/InputStreamReader
+	dup
+	getstatic	java/lang/System/in Ljava/io/InputStream;
+	invokespecial	java/io/InputStreamReader/<init>(Ljava/io/InputStream;)V
+	invokespecial	java/io/BufferedReader/<init>(Ljava/io/Reader;)V
+	invokevirtual	java/io/BufferedReader/readLine()Ljava/lang/String;
+ReadLineReturn:
+	areturn
+ReadLineCatch:
+	astore_0
+	ldc	"Fail"
+	areturn
+.catch	java/lang/Exception from ReadLineBegin to ReadLineReturn using ReadLineCatch
+.end method  
+
+.method public static f()I
+
+.limit locals 0
+.limit stack 5
+BeginGlobal:
+			ldc	0x5
+			ldc	0xA
+			imul
+		ldc	0x4
+		iadd
+	ireturn
+
+EndGlobal:
+.end method
+.method public static g(I)Ljava/lang/String;
+
+.limit locals 1
+.limit stack 5
+.var 0 is a I from BeginGlobal to EndGlobal
+BeginGlobal:
+	.line 6
+			iload	0
+			ldc	0x5
+			if_icmpeq	CmpEQ80792139
+			ldc	0x0
+			goto	CmpEQDone80792139
+		CmpEQ80792139:
+			ldc	0x1
+		CmpEQDone80792139:
+		ldc	0x1
+		if_icmpeq	If111812458
+		goto	IfElse111812458
+	If111812458:
+	.line 7
+		ldc	"hello"
+		areturn
+	IfElse111812458:
+	.line 9
+		ldc	"world"
+		areturn
+	IfDone111812458:
+
+EndGlobal:
+.end method
+.method public static main([Ljava/lang/String;)V
+
+.limit locals 2
+.limit stack 5
+BeginGlobal:
+.var 0 is s Ljava/lang/String; from BeginGlobal to EndGlobal
+	.line 14
+		getstatic	java/lang/System/out Ljava/io/PrintStream;
+		.line 14
+		invokestatic function2/f()I
+		invokevirtual	java/io/PrintStream/print(I)V
+
+
+	.line 15
+			ldc	0x4
+			ldc	0x5
+			imul
+		ldc	0x2
+		idiv
+	invokestatic function2/g(I)Ljava/lang/String;
+	astore	0
+
+	.line 16
+		getstatic	java/lang/System/out Ljava/io/PrintStream;
+		aload	0
+		invokevirtual	java/io/PrintStream/print(Ljava/lang/String;)V
+
+
+EndGlobal:
+return
+.end method
+