fix compiler error for build directory not existing

Author: kdschlosser

builder/esp32.py

@@ -40,6 +40,9 @@ def get_partition_file_name(otp):
 class Partition:
 
     def __init__(self):
+        if not os.path.exists('build'):
+            os.mkdir('build')
+
         self.save_file_path = f'"{SCRIPT_DIR}/build/partitions-{flash_size}MiB.csv"'
         self.first_offset = 0x9000
         self.nvs = 0x6000