don't allocate a 0B chunk of memory

Error: CLANG_WARNING:
rsyslog-7.4.10/runtime/ruleset.c:220:9: warning: Call to 'malloc' has an allocation size of 0 bytes
bugfix: don't leak memory returned by newActive()

Error: RESOURCE_LEAK (CWE-772):
rsyslog-7.4.10/runtime/ruleset.c:326: alloc_fn: Storage is returned from allocation function "newActive(batch_t *)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: alloc_fn: Storage is returned from allocation function "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: return_alloc_fn: Directly returning storage allocated by "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:326: var_assign: Assigning: "newAct" = storage returned from "newActive(pBatch)".
rsyslog-7.4.10/runtime/ruleset.c:362: leaked_storage: Variable "newAct" going out of scope leaks the storage it points to.

Error: RESOURCE_LEAK (CWE-772):
rsyslog-7.4.10/runtime/ruleset.c:373: alloc_fn: Storage is returned from allocation function "newActive(batch_t *)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: alloc_fn: Storage is returned from allocation function "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: return_alloc_fn: Directly returning storage allocated by "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:373: var_assign: Assigning: "newAct" = storage returned from "newActive(pBatch)".
rsyslog-7.4.10/runtime/ruleset.c:376: leaked_storage: Variable "newAct" going out of scope leaks the storage it points to.
bugfix: don't leak memory returned by newActive()

Error: RESOURCE_LEAK (CWE-772):
rsyslog-7.4.10/runtime/ruleset.c:506: alloc_fn: Storage is returned from allocation function "newActive(batch_t *)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: alloc_fn: Storage is returned from allocation function "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:220:2: return_alloc_fn: Directly returning storage allocated by "malloc(size_t)".
rsyslog-7.4.10/runtime/ruleset.c:506: var_assign: Assigning: "thenAct" = storage returned from "newActive(pBatch)".
rsyslog-7.4.10/runtime/ruleset.c:509: leaked_storage: Variable "thenAct" going out of scope leaks the storage it points to.
Merge branch 'v7-stable-rg-merges' into v8-stable-rg-merge

Conflicts:
	runtime/ruleset.c