decompiler: fixed incorrect method references from single letter classes

testData/results/TestMethodReferenceLetterClass.dec

@@ -0,0 +1,18 @@
+import java.util.function.Consumer;
+
+public class TestMethodReferenceLetterClass {
+   void boo() {
+      Consumer var1 = R::foo;// 21
+   }// 22
+}
+
+class 'TestMethodReferenceLetterClass' {
+   method 'boo ()V' {
+      5      4
+      6      5
+   }
+}
+
+Lines mapping:
+21 <-> 5
+22 <-> 6