Aquifer failes if box contain inactive cells

[hnil]

Minimal failing input case is generated by running 2D_FETKOVICAQUIFER.DATA modified as follows

--- 2D_FETKOVICHAQUIFER.DATA    2019-04-25 16:04:22.488901757 +0200
+++ 2D_FETKOVICHAQUIFER_ERROR.DATA  2019-04-25 16:02:00.923099073 +0200
@@ -99,6 +99,8 @@
 20*2575
 20*2600 /

+ACTNUM
+0 99*1/
 --------------------------------------------------------
 --
 --     Input of grid parametres
@@ -587,7 +589,7 @@

 AQUANCON
 -- Aq#     I1 I2  J1   J2  K1 K2 FACE
-  1      1  1  1    1   1  5  J- 1.0 1.0 NO/
+  1      1  4  1    1   1  5  J- 1.0 1.0 NO/
 --    1      1  33  1    33   1  2  J+  1.0 1.0 NO/
 --    1      1  33  1    33   1  2  I-  1.0 1.0 NO/
 --    1      1  33  1    33   1  2  I+  1.0 1.0 NO/

Diff generated by:

diff -u 2D_FETKOVICHAQUIFER.DATA 2D_FETKOVICHAQUIFER_ERROR.DATA

Then we get a run symptom like

flow 2D_FETKOVICHAQUIFER_ERROR.DATA --output-dir=test
**********************************************************************
*                                                                    *
*                      This is flow 2019.04-pre                      *
*                                                                    *
* Flow is a simulator for fully implicit three-phase black-oil flow, *
*             including solvent and polymer capabilities.            *
*          For more information, see https://opm-project.org         *
*                                                                    *
**********************************************************************

Reading deck file '2D_FETKOVICHAQUIFER_ERROR.DATA'
Program threw an exception: _Map_base::at

[GitPaean]

This issue will be closed through OPM/opm-common#1068.