fix the build of eigensolver_complex test.

it was calling the .value() method on an inner product, and that was blocked in bad zero-sized case.

fixed by adding the .value() method to DenseBase for all 1x1 expressions, and allowing coeff accessors in ProductBase for 1x1 expressions.

Eigen/src/Core/util/StaticAssert.h

@@ -92,7 +92,8 @@
         PACKET_ACCESS_REQUIRES_TO_HAVE_INNER_STRIDE_FIXED_TO_1,
         THIS_METHOD_IS_ONLY_FOR_SPECIFIC_TRANSFORMATIONS,
         YOU_CANNOT_MIX_ARRAYS_AND_MATRICES,
-        YOU_PERFORMED_AN_INVALID_TRANSFORMATION_CONVERSION
+        YOU_PERFORMED_AN_INVALID_TRANSFORMATION_CONVERSION,
+        THIS_METHOD_IS_ONLY_FOR_1x1_EXPRESSIONS
       };
     };
 
@@ -177,4 +178,9 @@
      EIGEN_PREDICATE_SAME_MATRIX_SIZE(TYPE0,TYPE1),\
     YOU_MIXED_MATRICES_OF_DIFFERENT_SIZES)
 
+#define EIGEN_STATIC_ASSERT_SIZE_1x1(TYPE) \
+      EIGEN_STATIC_ASSERT((TYPE::RowsAtCompileTime == 1 || TYPE::RowsAtCompileTime == Dynamic) && \
+                          (TYPE::ColsAtCompileTime == 1 || TYPE::ColsAtCompileTime == Dynamic), \
+                          THIS_METHOD_IS_ONLY_FOR_1x1_EXPRESSIONS)
+
 #endif // EIGEN_STATIC_ASSERT_H