Prevent unhandled exception in ModelBreakpoint
Prevent unhandled exception in ModelBreakpoint

Currently, ModelBreakpoint._updateInDebugger() assumes that it has a
non-null script, which isn't necessarily the case. This CL adds a check
to prevent it from trying to access properties on a null object.

Bug: 1019538
Change-Id: I70ed4d06c1c56d943e68a69a6563ebb2281e979c
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1983378
Reviewed-by: Robert Paveza <7787129de3d0cb4911c68d958db3023863584560@microsoft.com>
Reviewed-by: Brian Cui <eebe54f29fdfbfde69930c5ed5d840454db62ce7@microsoft.com>
Commit-Queue: Jack Lynch <d6fb7cfbb8c8618e756350219cb7952a0ad656b7@microsoft.com>

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