Do not start "knitting" until first line data is received

This actually lets us start selecting needles sooner than before, because
we no longer consider the needle that was current when the carriage was
detected to have been selected already.

src/ayab/knitter.cpp

@@ -238,10 +238,17 @@ bool Knitter::isReady() {
  */
 void Knitter::knit() {
   if (m_firstRun) {
+    if (m_currentLineNumber != 0) {        
+      // Request first line data before doing anything else
+      m_currentLineNumber = 0;
+      reqLine(m_currentLineNumber);
+      return;
+    } else if (m_lineRequested) {
+      // Still waiting for first line data: keep waiting
+      return;
+    }
+    // First line data received, let's proceed
     m_firstRun = false;
-    GlobalBeeper::finishedLine();
-    ++m_currentLineNumber;
-    reqLine(m_currentLineNumber);
   }
 
 #ifdef DBG_NOMACHINE