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.
bugfix: plug a memleak in rulesetProcessCnf()

Error: RESOURCE_LEAK (CWE-772):
rsyslog-7.4.10/runtime/ruleset.c:984: alloc_arg: "rulesetConstruct(ruleset_t **)" allocates memory that is stored into "pRuleset".
rsyslog-7.4.10/runtime/ruleset.c:729:1: alloc_fn: Storage is returned from allocation function "calloc(size_t, size_t)".
rsyslog-7.4.10/runtime/ruleset.c:729:1: var_assign: Assigning: "pThis" = "calloc(1UL, 56UL)".
rsyslog-7.4.10/runtime/ruleset.c:729:1: noescape: Resource "pThis" is not freed or pointed-to in function "rulesetInitialize(ruleset_t *)".
rsyslog-7.4.10/runtime/ruleset.c:726:1: noescape: "rulesetInitialize(ruleset_t *)" does not free or save its pointer parameter "pThis".
rsyslog-7.4.10/runtime/ruleset.c:729:1: var_assign: Assigning: "*ppThis" = "pThis".
rsyslog-7.4.10/runtime/ruleset.c:985: noescape: Resource "pRuleset" is not freed or pointed-to in function "rulesetSetName(ruleset_t *, uchar *)".
rsyslog-7.4.10/runtime/ruleset.c:638:43: noescape: "rulesetSetName(ruleset_t *, uchar *)" does not free or save its pointer parameter "pThis".
rsyslog-7.4.10/runtime/ruleset.c:1011: leaked_storage: Variable "pRuleset" going out of scope leaks the storage it points to.
fix regression from commit a955a9900629e2065e3ed1dd9d8f5a94e6faa7f0
fix regression (mem leak during normal operations) from commit b7a34ab022b4f427d0a73fc6ac37230e1ca29a84