Fix type instability in constructors.jl (#621)

Author: jondeuce

src/constructors.jl

@@ -117,7 +117,7 @@ function _default_Fun(f, d::Space)
         cf = default_Fun(f, d, 2^logn, Val(false))
         maxabsc = maximum(abs,cf.coefficients)
         if maxabsc == 0 && maxabsfr == 0
-            return zeros(d)
+            return zeros(T, d)
         end
 
         b = block(d,length(cf.coefficients))