stdlib: Fix fcvtbuf/ecvtbuf to handle inf/nan values

__dtoa returns a magic value in decpt (9999) for inf/nan values which
the fcvtbuf/ecvtbuf wrappers need to check for (as other __dtoa users
already do).

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

newlib/libc/stdlib/ecvtbuf.c

@@ -276,6 +276,12 @@ fcvtbuf (double invalue,
   if (!p)
     return NULL;
 
+  if (*decpt == 9999)
+    {
+      strcpy(fcvt_buf, p);
+      return fcvt_buf;
+    }
+
   /* Now copy */
 
   done = -*decpt;
@@ -327,6 +333,12 @@ ecvtbuf (double invalue,
   if (!p)
     return NULL;
 
+  if (*decpt == 9999)
+    {
+      strcpy(fcvt_buf, p);
+      return fcvt_buf;
+    }
+
   /* Now copy */
 
   while (p < end)