Fix vector pushes

MODULE.bazel

@@ -1,6 +1,6 @@
 module(
     name = "cpp_toolbelt",
-    version = "2.1.3",
+    version = "2.1.4",
 )
 
 bazel_dep(name = "platforms", version = "1.0.0")

toolbelt/payload_buffer.h

@@ -495,10 +495,14 @@ inline void PayloadBuffer::VectorPush(PayloadBuffer **self, VectorHeader *hdr,
     // the allocated block header (before the start of the memory)
     uint32_t *block = (*self)->ToAddress<uint32_t>(hdr->data);
     uint32_t current_size = DecodeSize(block);
-    if (current_size == total_size) {
-      // Need to double the size of the memory.
-      void *vecp = Realloc(self, block, 2 * hdr->num_elements * sizeof(T), true,
-                           enable_small_block);
+    const uint32_t needed = (hdr->num_elements + 1) * sizeof(T);
+    if (needed > current_size) {
+      // Grow to fit the next element; at least double prior capacity.
+      const uint32_t min_capacity =
+          2u * static_cast<uint32_t>(sizeof(T));
+      const uint32_t new_size = std::max<uint32_t>(
+          needed, std::max<uint32_t>(current_size * 2, min_capacity));
+      void *vecp = Realloc(self, block, new_size, true, enable_small_block);
       VectorHeader *new_hdr = (*self)->ToAddress<VectorHeader>(hdr_offset);
       new_hdr->data = (*self)->ToOffset(vecp);
       hdr = new_hdr;