emoji picker: Fix exceptions with regex characters in emoji filter.
emoji picker: Fix exceptions with regex characters in emoji filter.

Previously, the Zulip webapp would throw an exception if you used a
character like "+" in your search query, since we were using regular
expressions, when really we should have been just searching for
characters.

andersk/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,jackrzhang/zulip,verma-varsha/zulip,dhcrzf/zulip,rishig/zulip,andersk/zulip,jackrzhang/zulip,amanharitsh123/zulip,zulip/zulip,Galexrt/zulip,synicalsyntax/zulip,tommyip/zulip,hackerkid/zulip,Galexrt/zulip,tommyip/zulip,amanharitsh123/zulip,Galexrt/zulip,eeshangarg/zulip,zulip/zulip,timabbott/zulip,shubhamdhama/zulip,kou/zulip,dhcrzf/zulip,verma-varsha/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,rishig/zulip,shubhamdhama/zulip,amanharitsh123/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,shubhamdhama/zulip,mahim97/zulip,timabbott/zulip,jackrzhang/zulip,punchagan/zulip,rht/zulip,showell/zulip,andersk/zulip,rishig/zulip,jackrzhang/zulip,mahim97/zulip,kou/zulip,rht/zulip,jackrzhang/zulip,synicalsyntax/zulip,rishig/zulip,shubhamdhama/zulip,showell/zulip,synicalsyntax/zulip,brockwhittaker/zulip,synicalsyntax/zulip,tommyip/zulip,zulip/zulip,tommyip/zulip,rht/zulip,timabbott/zulip,shubhamdhama/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,rishig/zulip,timabbott/zulip,Galexrt/zulip,eeshangarg/zulip,hackerkid/zulip,vaidap/zulip,synicalsyntax/zulip,verma-varsha/zulip,brainwane/zulip,brainwane/zulip,dhcrzf/zulip,mahim97/zulip,tommyip/zulip,shubhamdhama/zulip,vaidap/zulip,kou/zulip,brainwane/zulip,hackerkid/zulip,timabbott/zulip,Galexrt/zulip,andersk/zulip,tommyip/zulip,synicalsyntax/zulip,verma-varsha/zulip,jackrzhang/zulip,brainwane/zulip,hackerkid/zulip,vaidap/zulip,showell/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,brockwhittaker/zulip,kou/zulip,amanharitsh123/zulip,rht/zulip,showell/zulip,eeshangarg/zulip,synicalsyntax/zulip,showell/zulip,verma-varsha/zulip,rishig/zulip,Galexrt/zulip,amanharitsh123/zulip,punchagan/zulip,mahim97/zulip,brainwane/zulip,zulip/zulip,punchagan/zulip,mahim97/zulip,rht/zulip,brockwhittaker/zulip,dhcrzf/zulip,brockwhittaker/zulip,rishig/zulip,jackrzhang/zulip,Galexrt/zulip,dhcrzf/zulip,brainwane/zulip,vaidap/zulip,brockwhittaker/zulip,amanharitsh123/zulip,vaidap/zulip,eeshangarg/zulip,hackerkid/zulip,tommyip/zulip,shubhamdhama/zulip,brainwane/zulip,verma-varsha/zulip,andersk/zulip,dhcrzf/zulip,kou/zulip,dhcrzf/zulip,zulip/zulip,mahim97/zulip,zulip/zulip,brockwhittaker/zulip,showell/zulip,vaidap/zulip