Solve bug in solution.jl

Proposed solution for bug in solution.jl (Fixes SciML#514). The solution handles the case where the basis of the problem is empty which would throw the DimensionMismatch error.

Author: girochat

src/solution.jl

@@ -34,7 +34,11 @@ function DataDrivenSolution(b::AbstractBasis, p::AbstractDataDrivenProblem,
     ps = get_parameter_values(b)
     prob = remake_problem(p, p = ps)
 
-    rss = sum(abs2, get_implicit_data(prob) .- b(prob))
+    if size(b(prob)) == size(get_implicit_data(prob))
+        rss = sum(abs2, get_implicit_data(prob) .- b(prob))
+    else
+        rss = sum(abs2, get_implicit_data(prob))
+    end
 
     return DataDrivenSolution{eltype(p)}(b,
         retcode,