[EventEngine] fix boundary conditions in memory allocation (#34047)

Ports https://github.com/grpc/grpc/pull/34003

src/core/lib/event_engine/posix_engine/posix_endpoint.cc

@@ -521,7 +521,7 @@ void PosixEndpointImpl::UpdateRcvLowat() {
 void PosixEndpointImpl::MaybeMakeReadSlices() {
   static const int kBigAlloc = 64 * 1024;
   static const int kSmallAlloc = 8 * 1024;
-  if (incoming_buffer_->Length() < static_cast<size_t>(min_progress_size_)) {
+  if (incoming_buffer_->Length() < std::max<size_t>(min_progress_size_, 1)) {
     size_t allocate_length = min_progress_size_;
     const size_t target_length = static_cast<size_t>(target_length_);
     // If memory pressure is low and we think there will be more than
@@ -531,8 +531,8 @@ void PosixEndpointImpl::MaybeMakeReadSlices() {
     if (low_memory_pressure && target_length > allocate_length) {
       allocate_length = target_length;
     }
-    int extra_wanted =
-        allocate_length - static_cast<int>(incoming_buffer_->Length());
+    int extra_wanted = std::max<int>(
+        1, allocate_length - static_cast<int>(incoming_buffer_->Length()));
     if (extra_wanted >=
         (low_memory_pressure ? kSmallAlloc * 3 / 2 : kBigAlloc)) {
       while (extra_wanted > 0) {