ras: don't assert because we try to allicate a huge vector

oss-fuzz/12915

src/imageformats/ras.cpp

@@ -121,6 +121,10 @@ static bool LoadRAS(QDataStream &s, const RasHeader &ras, QImage &img)
         qWarning() << "LoadRAS() mistmatch between height and width" << ras.Width << ras.Height << ras.Length << ras.Depth;
         return false;
     }
+    if (ras.Length > std::numeric_limits<int>::max()) {
+        qWarning() << "LoadRAS() unsupported image length in file header" << ras.Length;
+        return false;
+    }
 
     // each line must be a factor of 16 bits, so they may contain padding
     // this will be 1 if padding required, 0 otherwise