Fixed handling of multiple ret opcodes in GetFlow.

Hello..

I found out that the tests TestEnumPropertyEqualsFooOrElseEnumPropertyEqualsBar and TestEnumPropertyNotEqualsFooOrElseEnumPropertyEqualsBar would result in an ArgumentException when running with Release build active.

Seems like the generated IL with optimization had multiple returns, which made GetJoinPoint return wrong instruction:

         x => (x == TestEnum.Bar) || (x == TestEnum.Foo):

		[0]	IL_0000: ldarg.0	
		[1]	IL_0001: ldc.i4 2222	
		[2]	IL_0006: beq.s IL_0011	
		[3]	IL_0008: ldarg.0	
		[4]	IL_0009: ldc.i4 1111	
		[5]	IL_000e: ceq	
		[6]	IL_0010: ret	
		[7]	IL_0011: ldc.i4.1	
		[8]	IL_0012: ret	

I think I've fixed it by making GetFlow break when seeing a ret opcode, but this should probably be verified. At least it makes all tests OK when running on Release build.