Fix crash when specifiying -M and -A at once

Flags --asm and --mmap are incompatible. The compiler should
exit gracefully.

Author: boriel

tests/functional/test_cmdline.txt

@@ -0,0 +1,15 @@
+>>> from test_ import process_file
+>>> import os
+>>> os.environ['COLUMNS'] = '80'
+
+>>> process_file('arrbase1.bas', ['-q', '-S', '-O --asm', '-O --mmap arrbase1.map'])
+usage: zxb [-h] [-d] [-O OPTIMIZE] [-o OUTPUT_FILE] [-T] [-t] [-B] [-a] [-A]
+           [-S ORG] [-e STDERR] [--array-base ARRAY_BASE]
+           [--string-base STRING_BASE] [-Z] [-H HEAP_SIZE] [--debug-memory]
+           [--debug-array] [--strict-bool] [--enable-break] [-E] [--explicit]
+           [-D DEFINES] [-M MEMORY_MAP] [-i] [-I INCLUDE_PATH] [--strict]
+           [--headerless] [--version] [--parse-only]
+           [--append-binary APPEND_BINARY]
+           [--append-headless-binary APPEND_HEADLESS_BINARY]
+           PROGRAM
+zxb: error: Option --asm and --mmap cannot be used together

zxb.py

@@ -209,6 +209,10 @@ def main(args=None):
         parser.error('Option --append-binary needs either --tap or --tzx')
         return 5
 
+    if options.asm and options.memory_map:
+        parser.error('Option --asm and --mmap cannot be used together')
+        return 6
+
     OPTIONS.use_loader.value = options.basic
     OPTIONS.autorun.value = options.autorun
 
@@ -345,8 +349,9 @@ def main(args=None):
             return 5  # Error in assembly
 
     if OPTIONS.memory_map.value:
-        with open_file(OPTIONS.memory_map.value, 'wt', 'utf-8') as f:
-            f.write(asmparse.MEMORY.memory_map)
+        if asmparse.MEMORY is not None:
+            with open_file(OPTIONS.memory_map.value, 'wt', 'utf-8') as f:
+                f.write(asmparse.MEMORY.memory_map)
 
     return gl.has_errors  # Exit success