Do not NUL terminate base64 decoded output (#1752)

This is binary data and must use the explicit length.

src/string_util.cpp

@@ -438,7 +438,7 @@ unsigned char* s3fs_decode64(const char* input, size_t* plength)
     if(!input || 0 == strlen(input) || !plength){
         return NULL;
     }
-    result = new unsigned char[strlen(input) / 4 * 3 + 1];
+    result = new unsigned char[strlen(input) / 4 * 3];
 
     unsigned char parts[4];
     size_t input_len = strlen(input);
@@ -460,7 +460,6 @@ unsigned char* s3fs_decode64(const char* input, size_t* plength)
         }
         result[wpos++] = ((parts[2] << 6) & 0xc0) | (parts[3] & 0x3f);
     }
-    result[wpos] = '\0';
     *plength = wpos;
     return result;
 }