Fix the ossfuzz.c test module so that it does not segfault after a

"PRAGMA empty_result_callbacks=1;".  Add the ossshell.c program for
simple command-line testing of ossfuzz.c.

FossilOrigin-Name: 6f2d43eca68175ed28abae3afa792095af906af2

test/ossshell.c

@@ -0,0 +1,61 @@
+/*
+** This is a test interface for the ossfuzz.c module.  The ossfuzz.c module
+** is an adaptor for OSS-FUZZ.  (https://github.com/google/oss-fuzz)
+**
+** This program links against ossfuzz.c.  It reads files named on the
+** command line and passes them one by one into ossfuzz.c.
+*/
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "sqlite3.h"
+
+/*
+** The entry point in ossfuzz.c that this routine will be calling
+*/
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size);
+
+
+/*
+** Read files named on the command-line and invoke the fuzzer for
+** each one.
+*/
+int main(int argc, char **argv){
+  FILE *in;
+  int i;
+  int nErr = 0;
+  uint8_t *zBuf = 0;
+  size_t sz;
+
+  for(i=1; i<argc; i++){
+    const char *zFilename = argv[i];
+    in = fopen(zFilename, "rb");
+    if( in==0 ){
+      fprintf(stderr, "cannot open \"%s\"\n", zFilename);
+      nErr++;
+      continue;
+    }
+    fseek(in, 0, SEEK_END);
+    sz = ftell(in);
+    rewind(in);
+    zBuf = realloc(zBuf, sz);
+    if( zBuf==0 ){
+      fprintf(stderr, "cannot malloc() for %d bytes\n", (int)sz);
+      exit(1);
+    }
+    if( fread(zBuf, sz, 1, in)!=1 ){
+      fprintf(stderr, "cannot read %d bytes from \"%s\"\n",
+                       (int)sz, zFilename);
+      nErr++;
+    }else{
+      printf("%s... ", zFilename);
+      fflush(stdout);
+      (void)LLVMFuzzerTestOneInput(zBuf, sz);
+      printf("ok\n");
+    }
+    fclose(in);
+  }
+  free(zBuf);
+  return nErr;
+}