Fix indention level for --no-python-gen-numpy

[fliiiix]

Indention level is wrong. See minimal reproducer example:

monster_extra.fbs

table MonsterExtra {
  dvec : [double];
}

Generate with ./flatc --python --no-python-gen-numpy --gen-object-api monster_extra.fbs

without the fix

# MonsterExtraT
    def Pack(self, builder):
        if self.dvec is not None:
            MonsterExtraStartDvecVector(builder, len(self.dvec))
            for i in reversed(range(len(self.dvec))):
                builder.PrependFloat64(self.dvec[i])
                dvec = builder.EndVector()
        MonsterExtraStart(builder)
        if self.dvec is not None:
            MonsterExtraAddDvec(builder, dvec)
        monsterExtra = MonsterExtraEnd(builder)
        return monsterExtra

note the dvec = builder.EndVector() inside the loop

And with the fix ->

    # MonsterExtraT
    def Pack(self, builder):
        if self.dvec is not None:
            MonsterExtraStartDvecVector(builder, len(self.dvec))
            for i in reversed(range(len(self.dvec))):
                builder.PrependFloat64(self.dvec[i])
            dvec = builder.EndVector()
        MonsterExtraStart(builder)
        if self.dvec is not None:
            MonsterExtraAddDvec(builder, dvec)
        monsterExtra = MonsterExtraEnd(builder)
        return monsterExtra

[fliiiix]

//cc @jtdavis777 an other small fix easy to merge