eval: clear Parser instances before using

This prevents random values from the stack being used as
"variables" in expressions.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavutil/eval.c

@@ -461,7 +461,7 @@ int av_expr_parse(AVExpr **expr, const char *s,
                   const char * const *func2_names, double (* const *funcs2)(void *, double, double),
                   int log_offset, void *log_ctx)
 {
-    Parser p;
+    Parser p = { 0 };
     AVExpr *e = NULL;
     char *w = av_malloc(strlen(s) + 1);
     char *wp = w;
@@ -506,7 +506,7 @@ end:
 
 double av_expr_eval(AVExpr *e, const double *const_values, void *opaque)
 {
-    Parser p;
+    Parser p = { 0 };
 
     p.const_values = const_values;
     p.opaque     = opaque;

tests/ref/fate/eval

@@ -92,7 +92,7 @@ Evaluating 'st(1, 123); ld(1)'
 'st(1, 123); ld(1)' -> 123.000000
 
 Evaluating 'st(0, 1); while(lte(ld(0), 100), st(1, ld(1)+ld(0));st(0, ld(0)+1)); ld(1)'
-'st(0, 1); while(lte(ld(0), 100), st(1, ld(1)+ld(0));st(0, ld(0)+1)); ld(1)' -> 5073.000000
+'st(0, 1); while(lte(ld(0), 100), st(1, ld(1)+ld(0));st(0, ld(0)+1)); ld(1)' -> 4950.000000
 
 Evaluating 'st(1, 1); st(2, 2); st(0, 1); while(lte(ld(0),10), st(3, ld(1)+ld(2)); st(1, ld(2)); st(2, ld(3)); st(0, ld(0)+1)); ld(3)'
 'st(1, 1); st(2, 2); st(0, 1); while(lte(ld(0),10), st(3, ld(1)+ld(2)); st(1, ld(2)); st(2, ld(3)); st(0, ld(0)+1)); ld(3)' -> 144.000000