Passing size of 0 to malloc leads to assertion violation

This commit avoids the situation where size of 0 can be
passed to malloc. I think it does not alter the spirit
of the benchmark.

c/aws-c-common/aws_string_eq_byte_buf_harness.i

@@ -6860,7 +6860,7 @@ struct aws_string *ensure_string_is_allocated_nondet_length() {
 
 struct aws_string *ensure_string_is_allocated_bounded_length(size_t max_size) {
     size_t len = nondet_uint64_t();
-    assume_abort_if_not(len < max_size);
+    assume_abort_if_not(0 < len && len < max_size);
     return ensure_string_is_allocated(len);
 }
 

c/aws-c-common/aws_string_new_from_array_harness.i

@@ -9460,10 +9460,11 @@ struct aws_string *aws_string_clone_or_reuse(struct aws_allocator *allocator, co
 }
 void aws_string_new_from_array_harness() {
 
-    size_t alloc_size;
+    size_t alloc_size = nondet_size_t();
+    assume_abort_if_not(alloc_size > 0);
     uint8_t *array = bounded_malloc(alloc_size);
     struct aws_allocator *allocator = can_fail_allocator();
-    size_t reported_size;
+    size_t reported_size = nondet_size_t();
 
 
     assume_abort_if_not(reported_size <= alloc_size);