Fix int overflow in SVGSMILElement

Changed the casting of a float to not be reachable if the
input was fuzzed.

Bug: 980933, 949497
Change-Id: I6c47758bca6a8634c798708dda6956ec2b97f8d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1689551
Commit-Queue: Edvard Thörnros <edvardt@opera.com>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Auto-Submit: Edvard Thörnros <edvardt@opera.com>
Cr-Commit-Position: refs/heads/master@{#674991}