bionic: add missing NULL check from memory allocation on record_backtrace()

Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>

Change-Id: I739c63c5a7344fff1775580044dc647edf246ebf
diff --git a/libc/bionic/malloc_leak.c b/libc/bionic/malloc_leak.c
index 9796382..b21bc6a 100644
--- a/libc/bionic/malloc_leak.c
+++ b/libc/bionic/malloc_leak.c
@@ -323,6 +323,8 @@
     } else {
         // create a new entry
         entry = (HashEntry*)dlmalloc(sizeof(HashEntry) + numEntries*sizeof(intptr_t));
+        if (!entry)
+            return NULL;
         entry->allocations = 1;
         entry->slot = slot;
         entry->prev = NULL;