Skip android aar builds if no API header is available.

docker/base/build.sh

@@ -260,7 +260,11 @@ for TARGET in $TARGETS; do
 
       # Generate the JNI wrappers automatically with SWIG
       jni=`mktemp -d`
-      cp `find /build-android-aar | grep '\.h$' | head -n 1` $jni/$NAME.h
+      header=`find /build-android-aar | grep '\.h$' | head -n 1`
+      if [ "$header" == "" ]; then
+        echo "No API C header specified, skipping android-$PLATFORM/aar..."
+      else
+        cp $header $jni/$NAME.h
         sed -i -e 's|__complex|complex|g' $jni/$NAME.h
         sed -i -e 's|_Complex|complex|g' $jni/$NAME.h
         echo -e "%module $title\n%{\n#include \"$NAME.h\"\n%}\n%pragma(java) jniclasscode=%{\nstatic {\nSystem.loadLibrary(\"$NAME\");\n}\n%}\n%include \"$NAME.h\"" > $jni/$NAME.i
@@ -289,6 +293,7 @@ for TARGET in $TARGETS; do
         (cd $archive && zip -r $bundle *)
         rm -rf $jni $archive
       fi
+    fi
     # Clean up the android builds, toolchains and runtimes
     rm -rf /build-android-aar
     rm -rf /usr/local/go/pkg/android_*