A name followed by the same name with an trailing underscore results in `java.lang.NumberFormatException`

**Type of issue**: Bug Report

**Please provide the steps to reproduce the problem:**

Construct hardware with some name, then construct additional hardware with the same name followed by an underscore. For example:

```scala
package foobar

import chisel3._

class Foo extends Module {
val bar = RegInit(false.B)
val bar_ = RegInit(false.B)
}

object EmitFoo {
def main(args: Array[String]): Unit = {
(new chisel3.stage.ChiselStage).emitVerilog(new Foo)
}
}
```

**What is the current behavior?**

Fails, throws `java.lang.NumberFormatException`.

```
[info] running foobar.EmitFoo
[error] (run-main-0) java.lang.NumberFormatException: For input string: ""
[error] java.lang.NumberFormatException: For input string: ""
[error] at ... ()
[error] at ... ()
[error] at ... (Stack trace trimmed to user code only. Rerun with --full-stacktrace to see the full stack trace)
[error] stack trace is suppressed; run last Compile / bgRunMain for the full output
[error] Nonzero exit code: 1
[error] (Compile / runMain) Nonzero exit code: 1
```

**What is the expected behavior?**

Construct the appropriate hardware.

**Please tell us about your environment:**

Chisel version 3.5.6 and 3.6.0-RC2. Reproducible in the official Scastie environment of 3.6.0-RC2.

Does not reproduce in Chisel 3.5.5 and 3.5.4.

Official 3.6.0-RC2 Scastie:
https://scastie.scala-lang.org/jWaVv1vsSyGSG5I7Rvw9dw

3.5.6 Scastie:
https://scastie.scala-lang.org/fuqkiNCBTkCtnRWgJlLI2Q

**Other Information**

**What is the use case for changing the behavior?**

Chisel fails with a completely opaque error message.

Start with the Foo and EmitFoo reproducer, using ChiselStage.emitVerilog to confirm the failure when bar is followed by bar_. Trace the name handling that leads to NumberFormatException and compare behavior with Chisel 3.5.5. Done means the hardware is emitted successfully for the reproducer without the exception.

Written by the indexing model from the issue text.