[jfx17u] RFR: 8275138: WebView: UserAgent string is empty for first request

[Kevin Rushforth]

Clean backport to jfx17u

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Commit messages:
 - 8275138: WebView: UserAgent string is empty for first request

Changes: https://git.openjdk.java.net/jfx17u/pull/17/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx17u&pr=17&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275138
  Stats: 51 lines in 4 files changed: 33 ins; 0 del; 18 mod
  Patch: https://git.openjdk.java.net/jfx17u/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx17u pull/17/head:pull/17

PR: https://git.openjdk.java.net/jfx17u/pull/17