[TextServer] Add missing font mutex lock.
[TextServer] Add missing font mutex lock.

sanikoyes/godot,pkowal1982/godot,Valentactive/godot,firefly2442/godot,guilhermefelipecgs/godot,sanikoyes/godot,josempans/godot,ZuBsPaCe/godot,pkowal1982/godot,godotengine/godot,josempans/godot,sanikoyes/godot,godotengine/godot,BastiaanOlij/godot,akien-mga/godot,guilhermefelipecgs/godot,Zylann/godot,godotengine/godot,Valentactive/godot,Zylann/godot,Valentactive/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,vkbsb/godot,akien-mga/godot,firefly2442/godot,vkbsb/godot,akien-mga/godot,BastiaanOlij/godot,firefly2442/godot,guilhermefelipecgs/godot,Zylann/godot,guilhermefelipecgs/godot,godotengine/godot,Shockblast/godot,Shockblast/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,pkowal1982/godot,akien-mga/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,josempans/godot,firefly2442/godot,sanikoyes/godot,pkowal1982/godot,BastiaanOlij/godot,godotengine/godot,godotengine/godot,ZuBsPaCe/godot,Shockblast/godot,josempans/godot,guilhermefelipecgs/godot,Zylann/godot,Shockblast/godot,guilhermefelipecgs/godot,akien-mga/godot,BastiaanOlij/godot,Valentactive/godot,pkowal1982/godot,vkbsb/godot,godotengine/godot,josempans/godot,pkowal1982/godot,vkbsb/godot,pkowal1982/godot,sanikoyes/godot,firefly2442/godot,firefly2442/godot,vkbsb/godot,josempans/godot,sanikoyes/godot,Valentactive/godot,Zylann/godot,josempans/godot,vkbsb/godot,akien-mga/godot,BastiaanOlij/godot,Shockblast/godot,vkbsb/godot,josempans/godot,Shockblast/godot,Zylann/godot,Valentactive/godot,akien-mga/godot,ZuBsPaCe/godot,sanikoyes/godot,BastiaanOlij/godot,Zylann/godot,ZuBsPaCe/godot,firefly2442/godot,Shockblast/godot,sanikoyes/godot,ZuBsPaCe/godot,vkbsb/godot,pkowal1982/godot,godotengine/godot,firefly2442/godot,akien-mga/godot,Zylann/godot,Shockblast/godot,BastiaanOlij/godot,Valentactive/godot,Valentactive/godot