bug(ios): malformed context strings are possible

[sentry-io]

Sentry Issue: KEYMAN-IOS-GN

The data couldn’t be written because of an error in the content of the data.

[jahorton]

Stack trace:

  KeymanEngine        0x104abc90c  SentryManager.capture (SentryManager.swift:99)
  KeymanEngine        0x104abc90c  SentryManager.capture (SentryManager.swift:125)
  KeymanEngine        0x104abc90c  KeymanWebViewController.setContext (KeymanWebViewController.swift:271)
  KeymanEngine        0x104aaeaa8  InputViewController.setContextState (InputViewController.swift:631)
  KeymanEngine        0x104aaeaa8  InputViewController.textDidChange (InputViewController.swift:293)
  KeymanEngine        0x104aac310  InputViewController.textDidChange (<compiler-generated>)
  KeymanEngine        0x104aac310  InputViewController.textDidChange (<compiler-generated>:273)
  libdispatch         0x19723afa4  _dispatch_client_callout
  libdispatch         0x19724a8d0  _dispatch_async_and_wait_invoke
  libdispatch         0x19723afa4  _dispatch_client_callout

Currently with 23 events for a single user. Relevant breadcrumbing:

[...]
Setting lexical model: <lexicalModelID: "gff.ti.gff_tigrinya", languageID: "ti-er">
[...]
Setting language: <keyboardID: "gff_tigrinya_eritrea", languageID: "ti-er">
[...]

Note this line in the stacktrace:

  KeymanEngine        0x104abc90c  KeymanWebViewController.setContext (KeymanWebViewController.swift:271)

One simliar error has been reported before in assocation with JSON on iOS platforms:

• RCTJSONStringify() encountered the following error: The data couldn't be written because of an error in the content of the data facebook/react-native#14410

There also exist similar sounding errors, but with different wording at the end of the string.