improve GapBuffer test coverage

src/core/Buffer.cc

@@ -56,7 +56,7 @@ bool Buffer::load_from_file(const char * filename)
         return false;
     }
 
-    size_t buffer_size = ((unsigned long)file_size + 2u * System::page_size) & System::page_base_mask;
+    size_t buffer_size = ((unsigned long)file_size + System::page_size + (64u * 1024u)) & System::page_base_mask;
     uint8_t * buffer = (uint8_t *)System::alloc_pages(buffer_size >> System::page_size_log);
     if (buffer == NULL)
     {

src/core/GapBuffer.cc

@@ -4,7 +4,8 @@
 
 GapBuffer::GapBuffer()
 {
-    m_buffer = (uint8_t *)System::alloc_pages(1u);
+    int num_pages = (64u * 1024u + System::page_size - 1u) >> System::page_size_log;
+    m_buffer = (uint8_t *)System::alloc_pages(num_pages);
     m_buffer_size = System::page_size;
     m_size = 0u;
     m_gap_position = 0u;