also an ::Int typeassert for thisind

Author: nsajko

base/strings/basic.jl

@@ -446,7 +446,7 @@ ERROR: BoundsError: attempt to access 2-codeunit String at index [-1]
 [...]
 ```
 """
-thisind(s::AbstractString, i::Integer) = thisind(s, Int(i)::Int)
+thisind(s::AbstractString, i::Integer) = thisind(s, Int(i)::Int)::Int
 
 function thisind(s::AbstractString, i::Int)
     z = ncodeunits(s)::Int + 1