RFR: 6227536: KeyGenerator.init() methods do not throw IllegalArgumentException for keysize == 0 [v9]

[Kevin Driver]

> As mentioned in the bug report, this issue *should not* be a framework-level issue, since potentially an individual provider could create a keysize of zero to have a certain significance. 
> 
> In the changes made here for `HmacMD5`- and `HmacSHA1`- `KeyGenerator`s, the check is for `keysize <= 0` and this message indicates this is a check characteristic to the `SunJCE` provider.

Kevin Driver has updated the pull request incrementally with one additional commit since the last revision:

  put back standard if block, since we never hit the failure case

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9679/files
  - new: https://git.openjdk.org/jdk/pull/9679/files/d7542111..921fb976

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9679&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9679&range=07-08

  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9679.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9679/head:pull/9679

PR: https://git.openjdk.org/jdk/pull/9679