Fix nested #IF <cond> not working

Author: boriel

tests/functional/prepro91.bi

@@ -0,0 +1,9 @@
+
+#ifdef MACRO
+# if MACRO != VALUE
+   WRONG
+# endif
+#else
+   OK
+#endif
+

tests/functional/prepro91.out

@@ -0,0 +1,4 @@
+#line 1 "prepro91.bi"
+#line 7 "prepro91.bi"
+   OK
+#line 9 "prepro91.bi"

tests/functional/prepro92.bi

@@ -0,0 +1,9 @@
+
+REM Checks -D MACRO=VALUE is defined correctly from zxbc commandline
+
+#ifdef MACRO
+#  error This should not happen
+#else
+OK
+#endif
+

tests/functional/prepro92.out

@@ -0,0 +1,4 @@
+#line 1 "prepro92.bi"
+#line 7 "prepro92.bi"
+OK
+#line 9 "prepro92.bi"

tests/functional/prepro93.bi

@@ -0,0 +1,11 @@
+
+REM Checks -D MACRO=VALUE is defined correctly from zxbc commandline
+
+#ifdef MACRO
+#  if MACRO != VALUE
+#    error This should not happen
+#  endif
+#else
+OK
+#endif
+

tests/functional/prepro93.out

@@ -0,0 +1,4 @@
+#line 1 "prepro93.bi"
+#line 9 "prepro93.bi"
+OK
+#line 11 "prepro93.bi"

zxbpp/zxbpp.py

@@ -552,7 +552,8 @@ def p_if_expr_header(p):
     global ENABLED
 
     IFDEFS.append((ENABLED, p.lineno(1)))
-    ENABLED = bool(int(p[2])) if p[2].isdigit() else ID_TABLE.defined(p[2])
+    if ENABLED:
+        ENABLED = bool(int(p[2])) if p[2].isdigit() else ID_TABLE.defined(p[2])
 
 
 def p_expr(p):