Throwing-NULL check should only be triggered by --pointer-check

This check was introduced in d2713b2, with no particular reason that
it should be enabled unconditionally. The test included in that commit
has --pointer-check set, suggesting that this always was the desired
behaviour.

Author: tautschnig

jbmc/regression/jbmc/NullPointer3/conditional-check.desc

@@ -0,0 +1,9 @@
+CORE
+NullPointer3
+
+^VERIFICATION SUCCESSFUL$
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+^.*Null pointer check: FAILURE$

jbmc/src/java_bytecode/goto_check_java.cpp

@@ -1447,7 +1447,7 @@ void goto_check_javat::goto_check(
     else if(i.is_throw())
     {
       if(
-        i.get_code().get_statement() == ID_expression &&
+        enable_pointer_check && i.get_code().get_statement() == ID_expression &&
         i.get_code().operands().size() == 1 &&
         i.get_code().op0().operands().size() == 1)
       {

src/analyses/goto_check_c.cpp

@@ -2171,7 +2171,7 @@ void goto_check_ct::goto_check(
     else if(i.is_throw())
     {
       if(
-        i.get_code().get_statement() == ID_expression &&
+        enable_pointer_check && i.get_code().get_statement() == ID_expression &&
         i.get_code().operands().size() == 1 &&
         i.get_code().op0().operands().size() == 1)
       {