fix NULL dereference in fgetc/fputc when stream is NULL

Author: ZERICO2005

src/libc/fgetc.c

@@ -5,9 +5,12 @@ int __attribute__((weak)) fgetc(FILE *stream)
 {
     int c;
 
-    if (stream == NULL ||
-        stream == stdout ||
-        stream == stderr)
+    if (stream == NULL)
+    {
+        return EOF;
+    }
+
+    if (stream == stdout || stream == stderr)
     {
         c = EOF;
     }

src/libc/fputc.c

@@ -5,7 +5,12 @@ int __attribute__((weak)) fputc(int c, FILE *stream)
 {
     int ret;
 
-    if (stream == NULL || stream == stdin)
+    if (stream == NULL)
+    {
+        return EOF;
+    }
+
+    if (stream == stdin)
     {
         ret = EOF;
     }