Stop treating "/**/" as a Javadoc comment.

The Javadoc formatter rejects it.

Add a test for that plus another test.

MOE_MIGRATED_REVID=124240642

core/src/main/java/com/google/googlejavaformat/java/JavaInput.java

diff --git a/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java b/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
index 7b807ab..fa6eb9a 100644
--- a/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
+++ b/core/src/main/java/com/google/googlejavaformat/java/JavaInput.java
@@ -141,7 +141,7 @@
 
     @Override
     public boolean isJavadocComment() {
-      return text.startsWith("/**");
+      return text.startsWith("/**") && text.length() > 4;
     }
 
     @Override

core/src/test/java/com/google/googlejavaformat/java/GoogleJavadocFormattingTest.java

diff --git a/core/src/test/java/com/google/googlejavaformat/java/GoogleJavadocFormattingTest.java b/core/src/test/java/com/google/googlejavaformat/java/GoogleJavadocFormattingTest.java
index 4d65fbb..7462b7d 100644
--- a/core/src/test/java/com/google/googlejavaformat/java/GoogleJavadocFormattingTest.java
+++ b/core/src/test/java/com/google/googlejavaformat/java/GoogleJavadocFormattingTest.java
@@ -36,6 +36,19 @@
           new JavaFormatterOptions(JavadocFormatter.GOOGLE, Style.GOOGLE, SortImports.NO));
 
   @Test
+  public void notJavadoc() {
+    String[] input = {
+      "/**/", //
+      "class Test {}",
+    };
+    String[] expected = {
+      "/**/", //
+      "class Test {}",
+    };
+    doFormatTest(input, expected);
+  }
+
+  @Test
   public void empty() {
     String[] input = {
       "/***/", //
@@ -416,6 +429,21 @@
   }
 
   @Test
+  public void significantAsterisks() {
+    String[] input = {
+      "/** *", //
+      " * *",
+      " */",
+      "class Test {}",
+    };
+    String[] expected = {
+      "/** * * */", //
+      "class Test {}",
+    };
+    doFormatTest(input, expected);
+  }
+
+  @Test
   public void heading() {
     String[] input = {
       "/**", //