Fix associated false test (!81)

## What is the bug
Fix a test for the if_associated subroutine.
## How do you fix it
The false test did not pop up because of a bug in FortUTF. See #18



Approved-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Merged-by: Jonas Jucker <jonas.jucker@env.ethz.ch>
Changelog: bugfix

test/fortran/test_fortran_tools.f90

@@ -213,7 +213,7 @@ CONTAINS
     ptr => NULL()
     CALL TAG_TEST("Test_if_associated_false")
     output => if_associated(ptr)
-    CALL ASSERT_EQUAL(SIZE(output), 0)
+    CALL ASSERT_EQUAL(ASSOCIATED(output), .FALSE.)
 
     CALL TAG_TEST("Test_if_associated_false_else")
     output => if_associated(ptr, arr2)