avoid using EOF in the expression parser

src/runtime/c/pgf/expr.h

@@ -210,14 +210,14 @@ class PGF_INTERNAL_DECL PgfExprParser {
     const char *token_pos, *pos;
     uint32_t ch;
 
-    uint32_t getc();
+    bool getc();
     void putc(uint32_t ch);
 
 public:
     PgfExprParser(PgfText* input, PgfUnmarshaller *unmarshaller);
     ~PgfExprParser();
 
-    void str_char();
+    bool str_char();
     void token();
     bool lookahead(int ch);