[gnumeric] solver: check for non-numbers (errors, mostly) in target cell.

[Morten Welinder <mortenw src gnome org>]

commit 54fb2095cea404339e03a16e45d4c960f2b9efb4
Author: Morten Welinder <terra gnome org>
Date:   Wed Nov 11 16:05:54 2009 -0500

    solver: check for non-numbers (errors, mostly) in target cell.

 src/tools/solver/solver.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/tools/solver/solver.c b/src/tools/solver/solver.c
index f3bd6a4..54e3025 100644
--- a/src/tools/solver/solver.c
+++ b/src/tools/solver/solver.c
@@ -198,11 +198,13 @@ gnm_solver_param_valid (SolverParameters const *sp, GError **err)
 		return FALSE;
 	}
 
-	if (!gnm_cell_has_expr (target_cell)) {
+	if (!gnm_cell_has_expr (target_cell) ||
+	    target_cell->value == NULL ||
+	    !VALUE_IS_FLOAT (target_cell->value)) {
 		g_set_error (err,
 			     go_error_invalid (),
 			     0,
-			     _("Target cell, %s, must contain a formula"),
+			     _("Target cell, %s, must contain a formula that evaluates to a number"),
 			     cell_name (target_cell));
 		return FALSE;
 	}