add zero dim matmat/matvec-mul tests

src/host/linalg.jl

@@ -373,7 +373,7 @@ function generic_matmatmul!(C::AbstractArray{R}, A::AbstractArray{T}, B::Abstrac
         throw(DimensionMismatch("result C has dimensions $(size(C)), needs $((size(A,1),size(B,2)))"))
     end
     if isempty(A) || isempty(B)
-        return fill!(C, zero(R))
+        return rmul!(C, add.beta)
     end
 
     @kernel function matmatmul_kernel!(C, A, B)

test/testsuite/linalg.jl

@@ -420,6 +420,16 @@ end
             @test compare(mul!, AT, rand(T, 2,2), rand(T, 2,1), f(rand(T, 2)))
         end
     end
+
+    @testset "$T gemv zero-dim" for T in eltypes
+        y, A, x = rand(T, 4), rand(T, 4, 0), rand(T, 0)
+
+        @test compare(*, AT, A, x)
+        @test compare(mul!, AT, y, A, x)
+
+        y = rand(T, 4)
+        @test compare(mul!, AT, y, A, x, Ref(T(4)), Ref(T(5)))
+    end
 end
 
 @testsuite "linalg/mul!/matrix-matrix" (AT, eltypes)->begin
@@ -434,6 +444,16 @@ end
         @test compare(mul!, AT, C, f(A), g(B), Ref(T(4)), Ref(T(5)))
         @test typeof(AT(rand(T, 3, 3)) * AT(rand(T, 3, 3))) <: AbstractMatrix
     end
+
+    @testset "$T gemm zero-dim" for T in eltypes
+        A, B, C = rand(T, 4, 0), rand(T, 0, 4), rand(T, 4, 4)
+
+        @test compare(*, AT, A, B)
+        @test compare(mul!, AT, C, A, B)
+
+        C = rand(T, 4, 4)
+        @test compare(mul!, AT, C, A, B, Ref(T(4)), Ref(T(5)))
+    end
 end
 
 @testsuite "linalg/norm" (AT, eltypes)->begin